New Ag(I)-iminophosphorane coordination polymers as efficient catalysts precursors for the MW-assisted meyer-schuster rearrangement of propargylic alcohols in water

Article abstract of DOI:10.1021/ic400511d

Treatment of the N-thiophosphorylated iminophosphorane ligands (PTA)=NP(=S)(OR)₂ [PTA = 1,3,5-triaza-7-phosphaadamantane, 3a and 3b] and (DAPTA)=NP(=S)(OR)₂ [DAPTA = 3,7-diacetyl-1,3,7-triaza-5- bicyclo[3.3.1]nonane, 4a and 4b] with an equimolecular amount of AgSbF ₆ leads to high-yield formation of the new one-dimensional coordination polymers [Ag{μ²-N,S-(PTA)=NP(=S)(OR) ₂}]_x[SbF₆]_x (5a and 5b) and [Ag{μ²-O,S-(DAPTA)=NP(=S)(OR)₂}]_x[SbF ₆]_x (6a and 6b), respectively. These new (iminophosphorane)silver(I) coordination polymers are efficient catalyst precursors for the Meyer-Schuster isomerization of both terminal and internal alkynols. Reactions proceeded in water, under aerobic conditions and using microwave irradiation as heating source, to afford the corresponding α,β-unsaturated carbonyl compounds in excellent yields, without the addition of any cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min, 99%; 10th cycle 6 h, 97%). ESI-MS analysis of 5a in water has been carried out providing valuable insight into the monomeric active species responsible for catalytic activity in water.

Full text of DOI:10.1021/ic400511d

Article
pubs.acs.org/IC
New Ag(I)−Iminophosphorane Coordination Polymers as Efficient
Catalysts Precursors for the MW-Assisted Meyer−Schuster
Rearrangement of Propargylic Alcohols in Water
Joaquín García-Alvarez,* Josefina Díez, Cristian Vidal, and Cristian Vicent
,†
†
†
‡
́
†Laboratorio de Compuestos Organometal
Inorganica, Instituto Universitario de Química Organometal
E-33071, Oviedo, Spain
‡Serveis Centrals d’Instrumentacio
Científica, Universitat Jaume I, Avenida Sos Baynat s/n, 12071 Castello, Spain
́ ́
́
icos y Catal
́
isis (Unidad Asociada al CSIC), Departamento de Química Organ
́
ica e
́
́
ica “Enrique Moles”, Facultad de Química, Universidad de Oviedo,
S
* Supporting Information
ABSTRACT: Treatment of the N-thiophosphorylated iminophos-
phorane ligands (PTA)NP(S)(OR)2 [PTA = 1,3,5-triaza-7-
phosphaadamantane, 3a and 3b] and (DAPTA)NP(S)(OR)2
[DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]nonane, 4a and
4b] with an equimolecular amount of AgSbF6 leads to high-yield
formation of the new one-dimensional coordination polymers [Ag{μ2-
N,S-(PTA)NP(S)(OR)2}]x[SbF6]x (5a and 5b) and [Ag{μ2-O,S-
(DAPTA)NP(S)(OR)2}]x[SbF6]x (6a and 6b), respectively.
These new (iminophosphorane)silver(I) coordination polymers are
efficient catalyst precursors for the Meyer−Schuster isomerization of
both terminal and internal alkynols. Reactions proceeded in water,
under aerobic conditions and using microwave irradiation as heating
source, to afford the corresponding α,β-unsaturated carbonyl compounds in excellent yields, without the addition of any
cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min,
99%; 10th cycle 6 h, 97%). ESI-MS analysis of 5a in water has been carried out providing valuable insight into the monomeric
active species responsible for catalytic activity in water.
derivatives [i.e., DAPTA, 3,7-diacetyl-1,3,7-triaza-5-
bicyclo[3.3.1]nonane (2), Figure 1] have been previously
used as versatile building blocks for design of both one- and
two-dimensional coordination polymers.2 However, to our
knowledge, the ability of their iminophosphorane derivatives
[general formula (PTA)NR and (DAPTA)NR, respec-
tively] to act as the cornerstone piece for easy synthesis of new
coordination polymers has been totally neglected. In this sense,
we recently reported the synthesis of the first water-stable
iminophosphorane ligands based on the water-soluble
phosphines PTA and DAPTA [(PTA)NP(S)(OR)2 (R
= Et (3a), Ph (3b); (DAPTA)NP(S)(OR)2 (R = Et (4a),
Ph (4b), see Figure 1] as well as studying their coordination in
a Cu(I) precursor, yielding the corresponding one-dimensional
coordination polymers [Cu{μ2-N,S-(PTA)NP(S)-
(OR)2}2]x[PF6]x.3 These compounds have proved to be
efficient catalysts for copper-catalyzed cycloaddition of azides
and alkynes (both terminal and internal) in water and under
aerobic reaction conditions.3
INTRODUCTION
■
During the past decade, construction of new coordination
polymers has emerged as one of the most important research
topics due to their wide application in many fields such as
crystal engineering and coordination and materials chemistry,1
to name a few. In this sense, the water-soluble phosphine PTA
[1,3,5-triaza-7-phosphaadamantane (1), Figure 1] and its
On the other hand, the search for novel efficient organic
methodologies which proceed with high levels of selectivity and
Figure 1. Structure of ligands 3, 4a, and 4b and their Ag(I)-
coordination polymers 5a, 5b, 6a, and 6b.
Received: February 27, 2013
© XXXX American Chemical Society
A
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atom economy (i.e., all atoms of the reaction end up in the final
product) constitutes one of the major challenges in modern
synthesis.4 In this sense, isomerization reactions are typical
examples of atom economic processes as no byproducts are
generated. In this regard, isomerization reactions of propargylic
alcohols provide straightforward synthetic routes to α,β-
unsaturated carbonyl compounds which are (i) useful building
blocks in organic synthesis, (ii) advanced intermediates in the
manufacture of aromes and fragrances, and (iii) key structural
units in a large number of biologically active natural products.5
The isomerization process of these propargylic alcohols
proceeds through a formal 1,3-shift of the hydroxyl moiety,
known as the Meyer−Schuster rearrangement (Scheme 1).6
involving combination of these isomerization processes with
other well-established synthetic organic reactions.12−15
Despite the growing interest in this metal-catalyzed isomer-
ization reaction, efforts devoted to develop catalytic systems
able to operate in environmentally friendly solvents (i.e., water)
have been scarce. In fact, only a very limited number of active
catalysts in the Meyer−Schuster16 or Rupe17 rearrangement of
propargylic alcohols in water have been described to date in the
literature.18 This is particularly surprising considering (i) water
is a safe, a nontoxic, an eco-friendly, and a cheap solvent,19 (ii)
it may give rise to a completely new reactivity, and (iii) the
strong acceleration effect and regioselectivity of many organic
reactions in aqueous media have been previously reported.20
With these precedents in mind and continuing with our studies
aimed at exploiting the utility of new organometallic complexes
containing the iminophosphorane ligands 3a, 3b, 4a, and 4b in
metal-catalyzed organic reactions in water,3,21 herein we
describe (i) the synthesis and characterization of the new
one-dimensional Ag(I) coordination polymers [Ag{μ2-N,S-
(PTA)NP(S)(OR)2}]x[SbF6]x (5a and 5b) and [Ag{μ2-
O,S-(DAPTA)NP(S)(OR)2}]x[SbF6]x (6a and 6b), (ii)
the high catalytic activity of complex 5a for the regioselective
isomerization of propargylic alcohols into α,β-unsaturated
compounds with both terminal and internal alkynols, without
addition of any cocatalyst, in water, under microwave
irradiation and under air, and (iii) the recyclability of the
catalytic system in water (up to 10 consecutive runs).
Scheme 1. Meyer−Schuster and Rupe Rearrangements of
Propargylic Alcohols
RESULTS AND DISCUSSION
■
This method represents a significant upgrade to more
traditional protocols for synthesis of α,β-unsaturated carbonyl
compounds,7 which required the use of Brønsted acids under
harsh reaction conditions, leading usually to nonregioselective
transformations and poor functional group tolerance. In
particular, starting from substrates able to undergo a
competitive Rupe-type rearrangement (Scheme 1),8 non-
regioselective transformations are usually observed.9 In this
sense and with the gradual emergence of new catalysts, both the
Meyer−Schuster and the Rupe rearrangements have gained a
prominent role in organic synthesis,10 as clearly exemplified by
their implication in (i) synthetic protocols for total synthesis of
several natural organic products11 and (ii) tandem processes
Synthesis and Characterization of the New Silver(I)
Coordination Polymers [Ag{μ2-N,S-(PTA)NP(S)-
(OR)2}]x[SbF6]x (R = Et (5a), Ph (5b)) and [Ag{μ2-O,S-
(DAPTA)NP(S)(OR)2}]x[SbF6]x (R = Et (6a), Ph (6b)).
Following our previous interest on the design of Ag(I)
coordination polymers containing iminophosphorane ligands
[Ag{μ2-S,S-(CH2)n[P{NP(S)(OR)2}Ph2]2}]x[SbF6]x (n =
4, 6)]22 and our recent studies on coordination of the PTA−
iminophosphorane ligands,3,21 we decided to investigate
reaction of the iminophosphorane ligands 3a, 3b, 4a, and 4b
with a silver(I) precursor.23,24 In this sense, we found that
treatment of the silver(I) precursor AgSbF6 with a stoichio-
Scheme 2. Synthesis of the Silver(I) Complexes 5a, 5b, 6a, and 6b
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Figure 2. ORTEP-type view of the unit cell of compound 5b showing the crystallographic labeling scheme. Hydrogen atoms, aryl groups (except the
−
ipso carbons), and SbF6 anions have been omitted for clarity. Thermal ellipsoids are drawn at 10% probability level. Selected bond lengths
(Angstroms): Ag(1)−S(1) = 2.517(1); Ag(1)−S(1c) = 2.680(1); Ag(1)−Ag(1c) = 3.1548(8); Ag(1)−N(1b) = 2.301(4); P(1)−N(4) = 1.587(4);
N(4)−P(2) = 1.564(4); P(2)−S(1) = 1.990(2). Selected bond angles (degrees): S(1)−Ag(1)−S(1c) = 105.32(4); S(1)−Ag(1)−Ag(1c) =
50.31(3); S(1)−Ag(1c)−Ag(1) = 55.01(3); Ag(1)−S(1)−Ag(1c) = 74.68(4); P(1)−N(4)−P(2) = 127.0(3); N(4)−P(2)−S(1) = 115.1(2); P(2)−
S(1)−Ag(1) = 102.33(6); P(2)−S(1)−Ag(1c) = 115.56(7).
Figure 3. Part of the polymeric chain of complex 5b showing formation of alternated fused 4- and 14-membered rings (yellow = silver; pink = sulfur;
blue = nitrogen; orange = phosphorus; red = oxygen; gray = carbon).
Figure 4. ORTEP-type view of the unit cell of compound 6a showing the crystallographic labeling scheme. Hydrogen atoms, ethyl groups, the
(CH2)N(C(O)CH3)CH2 arm of the ligand 4a that does coordinate to the silver atoms, and the SbF6− anions have been omitted for clarity.
Thermal ellipsoids are drawn at 10% probability level. Selected bond lengths (Angstroms): Ag(1)−S(1) = 2.515(3); Ag(1)−S(4) = 2.531(3);
Ag(2)−S(1) = 2.371(3); Ag(2)−S(2) = 2.391(3); Ag(3)−S(2) = 2.607(3); Ag(3)−S(3) = 2.606(3); Ag(4)−S(3) = 2.405(3); Ag(4)−S(4) =
2.389(3); Ag(1)−O(8) = 2.384(7); Ag(1)−O(9) = 2.394(8); Ag(3)−O(4) = 2.346(8); Ag(3)−O(16) = 2.339(8); Ag(1)−Ag(2) = 3.124(1);
Ag(1)−Ag(4) = 3.015(1); Ag(2)−Ag(4) = 3.074(2); P(1)−N(4) = 1.58(1); P(2)−N(4) = 1.57(1); P(3)−N(5) = 1.56(1); P(4)−N(5) = 1.576(9);
P(5)−N(10) = 1.589(9); P(6)−N(10) = 1.555(9); P(7)−N(13) = 1.575(9); P(8)−N(13) = 1.58(1); C(8)−O(4) = 1.25(1); C(25)−O(8) =
1.24(1); C(26)−O(9) = 1.24(1); C(51)−O(16) = 1.23(1). Selected bond angles (degrees): S(1)−Ag(1)−S(4) = 150.5(1); Ag(1)−S(4)−Ag(4) =
75.54(9); S(4)−Ag(4)−S(3) = 164.9(1); Ag(4)−S(3)−Ag(3) = 102.3(1); S(3)−Ag(3)−S(2) = 96.71(9); Ag(3)−S(2)−Ag(2) = 102.8(2); S(2)−
Ag(2)−S(1) = 167.6(1); S(1)−Ag(1)−O(8) = 114.3(2); S(1)−Ag(1)−O(9) = 87.0(2); S(4)−Ag(1)−O(8) = 89.0(2); S(4)−Ag(1)−O(9) =
115.5(2); O(8)−Ag(1)−O(9) = 81.2(3); S(2)−Ag(3)−O(4) = 129.0(2); S(2)−Ag(3)−O(16) = 108.0(2); S(3)−Ag(3)−O(4) = 112.3(2); S(3)−
Ag(3)−O(16) = 132.6(2); O(4)−Ag(3)−O(16) = 82.6(3).
metric amount of the PTA-based iminophosphorane ligands 3a
and 3b, in dichloromethane at room temperature, leads to
selective formation of polymeric complexes [Ag{μ2-N,S-
(PTA)NP(S)(OR)2}]x[SbF6]x (R = Et (5a), Ph (5b);
76−79%, Scheme 2). Both 5a and 5b are formed via selective
bidentate (i) S-coordination of the N-thiophosphoryl fragment
and (ii) N-coordination of one nitrogen atom from the
adamantane ring. In contrast, the DAPTA-base iminophos-
phorane ligands 4a and 4b containing carbonyl groups (C(
O)CH3) generate, under the same reaction conditions, new
polymeric derivatives [Ag{μ2-O,S-(DAPTA)NP(S)-
(OR)2}]x[SbF6]x (R = Et (6a), Ph (6b); 87−91%, Scheme
2) via selective bidentate (i) S-coordination of the N-
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Figure 5. Core of the polymeric double chain of complex 6a showing only the atoms involved in the chain (yellow = silver; pink = sulfur; blue =
nitrogen; orange = phosphorus; red = oxygen; gray = carbon).
thiophosphoryl fragment and in this case (ii) O-coordination of
the oxygen atom of the C(O)CH3 unit.
(i) the silver(I) complex [Ag(PTA)(H2O)][NO3] (Ag−N =
2.441(4) and 2.468(4) Å) with tridentate P,N,N′-coordinated
PTA in a polymeric net structure2b and (ii) the mixed-metal
Ag(I)/Ru(II) water-soluble organometallic polymer [CpRu-
(H2O)(μ2-P,N-PTA)2AgCl2]x (Ag−N = 2.423(6) Å).2a
Compounds 5a, 5b, 6a, and 6b have been isolated in high
yields as air- and light-stable white solids that behave as 1:1
electrolytes in acetone solutions (ΛM = 105−115
Ω−1·cm−2·mol−1). As we previously described for the
iminophosphorane Cu(I) coordination polymers [Cu{μ2-N,S-
(PTA)NP(S)(OR)2}2]x[PF6]x,3 we found that only
complexes 5 and 6a, which contain ethyl groups in the N-
thiophosphorylated units −P(S)(OEt)2, were soluble in
water (S25 °C values of 5.0 and 7.0 mg mL−1, respectively), while
complexes 5 and 6b were scarcely soluble in water. Complexes
5a, 5b, 6a, and 6b have been characterized by means of
Remarkably, intermolecular silver−sulfur interactions take
place leading to a polymeric chain with alternating 14-
membered (Ag−S−P−N−P−C−N−Ag-S−P−N−P−C−N)
and 4-membered (Ag−S−Ag−S) dimetalla fused rings (see
Figure 3). The Ag(1)−S(1c) (2.680(1) Å) bond length can be
reasonably regarded as a real bonding interaction since it falls
within the accepted range for single Ag−S bonds (ca. 2.2−3.0
Å).22,26 A weak silver−silver contact is also present in the
polymer (Ag(1)−Ag(1a) = 3.1548(8) Å).27 The existence of all
these intermolecular bonding interactions is clearly reflected in
the S(1)−Ag(1)−S(1c) angle, which deviates considerably
from the expected linearity (105.32(4)°). It is also interesting
to note that bond distances within the PN−PS framework
are almost identical (ca. 0.02 Å) to those found in the
structure of the free ligand 3b,3 indicating that electronic
delocalization of the nitrogen lone pair is maintained upon
coordination of the thiophosphoryl unit to the metal.
In contrast to 5b, the unit cell of complex 6a corresponds to
the fragment [Ag{μ2 -S,O-(DAPTA)NP(S)-
(OEt)2]12[SbF6]12 (see Figure 4), which contains 12 silver
atoms and 12 ligands (DAPTA)NP(S)(OEt)2 (4a).
Selective μ2-S,O coordination of the N-thiophosphoryl
((EtO)2PS) and carbonylic (C(O)CH3) units of the
iminophosphorane ligand 4a is observed, which acts as a bridge
between the silver atoms, while the nitrogen atoms of the
aminophosphine remain uncoordinated. To our knowledge, 6a
represents the first example of an organometallic complex that
shows O-coordination of DAPTA to a metal.28 X-ray
crystallographic analysis revealed formation of an eight-
membered ring (Ag−S−Ag−S−Ag−S−Ag−S)29 in which
three of the silver atoms (Ag(1), Ag(2), and Ag(4)) are closer
[with small Ag−S interactions; Ag(1)−S(1) = 2.514(3) Å,
Ag(1)−S(4) = 2.531(3) Å, Ag(2)−S(1) = 2.371(3) Å, Ag(4)−
S(4) = 2.389(3) Å], adopting a triangle-like disposition,30 while
the fourth silver atom (Ag(3)) is located further away, bridged
to the Ag(2) and Ag(4) atoms by a longer Ag−S interaction
(Ag(3)−S(2) = 2.607(3) Å, Ag(3)−S(3) = 2.606(3) Å). All
these Ag−S contacts compare well with those previously
described for the polymeric structure of the Ag(I) complex 5b
(see caption of Figure 2). The three Ag−Ag bond lengths
[Ag(1)−Ag(2) = 3.124(1) Å, Ag(2)−Ag(4) = 3.074(1) Å,
Ag(4)−Ag(1) = 3.015(1) Å] are consistent with the presence
of weak silver−silver contacts as in polymer 5b.27 It should be
noticed that the central silver atoms (Ag(2) and Ag(4)) of the
eight-membered ring adopt a pseudolinear arrangement [S(1)−
Ag(2)−S(2) = 167.6(1)° and S(3)−Ag(4)−S(4) = 164.9(1)°],
while the terminal silver atoms display a distorted tetrahedral
geometry [subtending bond angles from 82.6(3)° (O(4)−
Ag(3)−O(16)) to 132.6(2)° (O(16)−Ag(3)−S(3)) (mean
110.2°) for Ag(3) and from 81.2(3)° (O(8)−Ag(1)−O(9)) to
1
standard spectroscopic techniques [IR and 31P{1H}, H, and
13C{1H} NMR] and elemental analysis, which support the
proposed formulations. Complexation of ligands 3a, 3b, 4a, and
4b to silver is reflected in the 31P{1H} NMR spectra of 5a, 5b,
6a, and 6b (see Experimental Section) by slight variations in
the PN [Δδ = 3−9 ppm; δP = −31.94 to −10.92 ppm] and
(RO)2PS [Δδ = 2−5 ppm; δP = 49.90−55.46 ppm]
resonances. As expected, 1H and 13C{1H} NMR spectra display
the corresponding phosphine backbone signals of PTA and
DAPTA. The observed preference for S- vs N-coordination of
the iminophosphoranyl units PN−P(S)(OR)2 in com-
plexes 5a, 5b, 6a, and 6b is in complete accord with the well-
known coordination chemistry of N-thiophosphorylated
iminophosphoranes R3PN−PS(OR)2, which is almost
entirely dominated by coordination of the sulfur atom.25
Although formation of formally 1:1 adducts of the starting
reagents [AgSbF6·ligand] is readily deduced from their
elemental analysis (details are given in Experimental Section),
the real nature of these complexes could only be determined by
single-crystal X-ray diffraction methods. Drawings of the unit
cell and polymeric chains of complexes 5b and 6a are shown in
Figures 2−4; selected bonding parameters for 5b and 6a are
listed in the captions of Figures 2 and 4, respectively.
Concerning the structure of complex 5b (see Figure 2), the
unit cell corresponds to the fragment [Ag{μ2-N,S-(PTA)
NP(S)(OR)2}]4[SbF6]4 containing four silver atoms and
four ligands (PTA)NP(S)(OPh)2 (3b), which gives rise to
a polymeric double chain along the z axis. Thus, this X-ray
analysis unambiguously confirms formation of a 14-membered
dimetalla ring formed by two silver atoms bridged by two
iminophosphorane ligands in a head-to-tail conformation. The
coordination sphere around silver consists of (i) one S-
coordinated (PhO)2PS unit, as suggested by the 31P{1H}
NMR data, and (ii) one N-coordinated amino group from the
aminophosphine ring. The Ag(1)−S(1) (2.517(1) Å) bond
length inside the 14-membered dimetalla ring is longer than
those previously described for Ag(I) complexes containing S-
coordinated N-thiophosphorylated bis(iminophosphorane)
ligands22 (Ag−S = 2.324(3)−2.449(2) Å) but compare well
with those shown by Ag(I) complexes containing S-coordinated
phosphine−sulfides.26 In contrast, the Ag(1)−N(1b) (2.301(4)
Å) bond length is smaller than those previously described for
D
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150.5(1)° (S(1)−Ag(1)−S(4)) (mean 106.3°) for Ag(1))].
These tetracoordinated silver(I) atoms (Ag(3) and Ag(1))
allow the connection of two eight-membered rings (Ag4S4)
through the O-coordination of the carbonylic unit (C(
O)CH3) of the iminophosphorane ligand 4a, giving rise to a
polymeric double chain (see Figure 5) along the y axis. The
Ag−O bond lengths [from 2.339(8) Å for Ag(3)−O(16) to
2.394(8) Å for Ag(1)−O(9)] fall within the previously
reported values for silver(I) complexes containing O-coordi-
nated carbonylic (NC(O)R) fragments.31 As we have
previously seen in the case of the free iminophosphorane
ligands3 and in the aforementioned polymeric Ag(I) complex
5b (see Figure 2), the bond distances within the PN−PS
framework are again almost identical (ca. 0.02 Å, see caption
to Figure 4), indicating that electronic delocalization of the
nitrogen lone pair is maintained upon coordination of the
thiophosphoryl unit to the metal. As expected, the CO bond
distances in 6b [from 1.23(1) (C(51)−O(16) to 1.24(1) Å
(C(8)−O(4)] are slightly longer than those previously
observed in the free ligand 4b (ca. 1.222 Å).3
In order to gain more information about the integrity and
nature of the species present in aqueous solution, electrospray
ionization (ESI) mass spectrometric measurements of a
solution of 5a in water were performed.32 Positive ESI mass
spectra recorded upon gentle ionization conditions (cone
voltage Uc = 10 V) revealed the presence of a variety of Ag-
containing species readily identified on the basis of their
characteristic isotopic pattern. The base peak corresponds to
the [Ag{(PTA)NP(S)(OEt)2}2]+ cation at m/z 755.0, and
additional (i) monomeric species formulated as [Ag{(PTA)
NP(S)(OEt)2}]+ (m/z 431.0) and [Ag{(PTA)NP(
S)(OEt)2}(H2O)]+ (m/z = 449.0) (ii) and dimeric
[Ag2{(PTA)NP(S)(OEt)2}3]2+ (m/z 593.0) were also
observed. Assignments were based on accurate m/z determi-
nations as well as comparison of simulated an experimental
isotopic pattern (see Figures ESI-1 and ESI-2 in the
Supporting Information). Interestingly, mononuclear com-
plexes were observed as dominant species in solution,
suggesting that unlike in the solid state complex 5a is
dismantled in aqueous solution to give predominantly
monomeric species. It is apparent that these monomeric
species are readily formed and therefore can be proposed as the
active catalytic species in aqueous medium (see below).
Isomerization of Propargylic Alcohols into α,β-
Unsaturated Carbonyl Compounds Catalyzed by the
Cationic Ag(I) Compound [Ag{μ2-N,S-(PTA)NP(S)-
(OEt)2}]x[SbF6]x (5a). Although in recent years Ag(I)
complexes containing water-soluble PTA ligands have been
screened for their potential antimicrobial activity2j,24 and
luminescent properties,2i their applications as catalysts for
organic transformations in water are virtually unknown.33 With
this precedent in mind, we decided to test the silver(I)
coordination polymers 5a, 5b, 6a, and 6b as potential catalyst
precursors in the Meyer−Schuster rearrangement of prop-
argylic alcohols in aqueous media34,35 using the isomerization
of the commercially available 1,1-diphenyl-2-propyn-1-ol (7a)
into 3,3-diphenylpropenal (8a) as a model reaction (see
Scheme 3). Thus, in a typical experiment, the corresponding
Ag(I) precursor (1 mol % of Ag) and the propargylic alcohol 7a
were added to 1 mL of water under air using as the heating
source microwave irradiation at 160 °C,36 the course of the
reaction being monitored by gas chromatography. Pleasingly, all
Ag(I) complexes tested were found to be active and selective
Scheme 3. Ag(I)-Catalyzed Isomerization of 1,1-Diphenyl-2-
propyn-1-ol (7a) to 3,3-Diphenylpropenal (8a) Catalyzed by
Complexes 5a, 5b, 6a, and 6b
a
a
Reactions were performed under air with microwave irradiation at
160 °C in water and using 1 mmol of the alkynol 7a. [Substrate]/[Ag]
ratio = 100:1.
catalysts in water, affording 3,3-diphenylpropenal (8a) as the
unique reaction product. Interestingly, the catalytic activity of
complex 5a (containing the ligand PTA−iminophosphorane) is
higher than that of complex 6a (containing the ligand
DAPTA−iminophosphorane) [45 min (99%) vs 1.5 h
(97%)]. A similar catalytic trend has also been found in their
water-insoluble counterpart catalysts 5b and 6b [1 h (98%) vs 3
h (96%)], demonstrating the influence of the iminophosphor-
ane ligand on the reaction rate. The presence of catalytic
amounts of silver(I) complexes 5a, 5b, 6a, and 6b was found to
be essential as no isomerization reaction was observed in their
absence. Use of other reaction conditions (like, for example,
conventional heating, lower temperatures, and/or lower catalyst
loadings) slowed down the reaction considerably; as an
example, using 1 mol % of complex 5a in refluxing water,
20% conversion of 1,1-diphenyl-2-propyn-1-ol into 3,3-
diphenylpropenal was only achieved after 24 h. At this point
it should be noticed that under similar reactions conditions (1
mol % of catalyst loading, in water, at 160 °C, and under
microwave irradiation) InCl3 is able to catalyze the isomer-
ization reaction of the alkynol 7a into the corresponding enal
8a in a shorter reaction time (5 min).16h
Under these optimized reaction conditions, the most active
Ag(I) complex [Ag{μ2 -N, S-(PTA) NP (S)-
(OEt)2}]x[SbF6]x (5a) was found to be an efficient catalyst
precursor for selective isomerization of a large number of other
terminal propargylic alcohols, highlighting the wide substrate
scope and synthetic utility of this catalytic transformation.
Thus, as observed for 1,1-diphenyl-2-propyn-1-ol (entry 1 in
Table 1), other tertiary alkynols 7b−f underwent selective
isomerization into the corresponding enals 8b−f, which could
be isolated after appropriate chromatographic workup in
excellent yields (91−95%; entries 1−5 in Table 1). An
influence of the electronic properties of the aryl rings on the
reaction rates was observed. Thus, alkynols with electron-
withdrawing groups showed less reactivity (entry 4) as
compared to substrates with electron-donating substituents
(entry 5). It is important to note that for the propargylic
alcohol 2-phenyl-3-butyn-2-ol (7f, entry 6), in which the
isomerization process can proceed through the competitive
Rupe-type rearrangement to generate the corresponding α,β-
unsaturated enone (see Scheme 1), exclusive formation of the
α,β-unsaturated enal 8f as a mixture of the corresponding E and
Z stereoisomers in a ca. 3:2 ratio was observed.37 Secondary
terminal alkynols (entries 7 and 8, Table 1) can also be
efficiently and selectively isomerized into the corresponding
enals using complex [Ag{μ2-N,S-(PTA)NP(S)-
(OEt)2}]x[SbF6]x (5a) as catalyst in water. Again, reactions
proceeded to completion in the absence of any cocatalyst.
Interestingly, resulting enals 7g−h were exclusively obtained as
the thermodynamically more stable E isomers.38
E
dx.doi.org/10.1021/ic400511d | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Isomerization of Terminal Propargylic Alcohols
Table 2. Isomerization of Internal Propargylic Alcohols 9a−
d into Enones 10a−d Catalyzed by Complex [Ag{μ2-N,S-
7a−h into Enals 8a−h Catalyzed by Complex [Ag{μ2-N,S-
a
a
(PTA)NP(S)(OEt)2}]x[SbF6]x (5a) in Water
(PTA)NP(S)(OEt)2}]x[SbF6]x (5a) in Water
T
T
b
b
entry
substrate 7
R1 = R2 = Ph (7a)
[min]
yield of 8
entry
substrate 9
R1 = R2 = R3 = Ph (9a)
R1 = Me; R2 = Ph; R3 = H (9b)
R1 = Me; R2 = 4-C6H4OMe; R3 = H (9c)
R1 = Ph; R2 = Ph; R3 = H (9d)
[min]
yield of 10
1
2
3
4
5
6
7
8
45
8a; 99 (95)
8b; 95 (91)
8c; 97 (92)
8d; 99 (95)
8e; 98 (93)
1
2
3
4
15
60
90
30
10a; 99 (92)
10b; 96 (90)
10c; 96 (91)
10d; 99 (94)
R1R2 = 2,2′-C6H4−C6H4 (7b)
R1R2 = 2,2′-C6H4CHCHC6H4 (7c)
R1 = R2 = 4-C6H4F (7d)
30
30
300
15
R1 = R2 = 4-C6H4Me(7e)
a
Reactions were performed under air in a CEM Discover S-Class
microwave synthesizer at 160 °C through moderation of the initial
power (300 W). A 1 mmol amount of the corresponding alkynol was
used (1 mL of water). [Substrate]/[Ag] ratio = 100:1. Determined by
GC. Isolated yields after chromatographic workup are given in
brackets.
c
R1 = Ph, R2 = Me (7f)
90
8f; 97 (91)
8g; 99 (91)
8h; 97 (93)
R1 = Ph, R2 = H (7g)
300
240
b
R1 = 2-naphthyl, R2 = H (7h)
a
Reactions were performed under air in a CEM Discover S-Class
microwave synthesizer at 160 °C through moderation of the initial
power (300 W). A 1 mmol amount of the corresponding alkynol was
b
used (1 mL of water). [Substrate]/[Ag] ratio = 100:1. Determined by
GC. Isolated yields after chromatographic workup are given in
brackets. A mixture of E and Z isomers in ca. 3:2 ratio is formed.
groups on the propargylic alcohol were more reactive than
propargylic alcohols with electron-poor aryl groups (see Table
1).10
c
It is well known that one of the major advantages associated
with the use of water as reaction media in metal-catalyzed
organic reactions is the possibility of recycling the catalyst
previous separation of the organic product formed by simple
extraction with organic solvents (without the need of
recovering the catalyst; see the general procedure for catalyst
recycling in the Supporting Information).20 In addition, the
lifetime of a catalytic system and its level of reusability are very
important factors.43 Thus, under the aforementioned reaction
conditions (Tables 1 and 2) and using as a model reaction
isomerization of the propargylic alcohol 7a, we found that the
catalytic system remains active (97−99% yield) after recycling
up to 10 consecutive times (see Table 3) with a gradual
decrease of the activity after each recycling. Thus, for the first
five cycles less than 2 h was needed to achieve quantitative
conversion, while more than 3 h was required after the fifth
cycle, probably due to both leaching during workup and
decomposition of the catalyst.
Use of MW heating has received considerable attention as a
new method for one-pot synthesis of silver nanostructures in
solution.39 In all the catalytic reactions listed in Table 1,
formation of silver nanoparticles was studied by means of TEM
(transmission electron microscopy) or SEM/EDX (scanning
electron microscopy/energy-dispersive X-ray spectroscopy)
techniques (see Supporting Information), and silver nano-
particles were detected in the reaction (see Supplementary
Infomation). Thus and in order to determine whether the
process is really homogeneous, isomerization of the propargylic
alcohol 7a into the enal 8a promoted by the silver(I) complex
5a, in the presence of Hg, was studied. The Hg-poisoned
catalytic reactions proceed with the same conversion (99%, 45
min), thus suggesting that the formed silver nanoparticles do
not play a role in this catalytic transformation. This Hg(0)-
poisoning test is the most direct method to distinguishing
homogeneous from heterogeneous catalysis when transition
metals able to form an amalgam are employed.40 In line with
this, the isolated silver nanoparticles generated from complex
5a showed no catalytic activity toward formation of the desired
enal 8a. These experimental facts seem to indicate that possible
catalysis by silver nanoparticles is not involved in this
isomerization process.
Table 3. Ag(I)-Catalyzed Isomerization of the Propargylic
a
Alcohol 7a into Enal 8a in Water: Catalyst Recycling
Finally, and as shown in Table 2, it is also worth noting that
the activity of complex 5a is not restricted to terminal alkynols,
as the internal propargylic alcohols 9a−d can be also efficiently
transformed into the corresponding enones 10a−d. As
previously observed, complete E stereoselectivity was once
again reached starting from secondary alcohols. The limitation
of this methodology concerns the use of primary propargylic
alcohols RCCCH2OH, which under standard reaction
conditions give rise to intractable polymeric materials.41 The
observed catalytic activity of complex 5a with internal alkynols
seems to indicate that silver(I) hydroxyvinylidene derivatives
are not involved as key intermediate complexes in this
isomerization reaction.42 In this sense, a possible dehydra-
tion/hydration sequence through a carbocation intermediate is
in accord with the experimental fact that electron-rich aryl
b
c
c
cycle T [min] yield
TON
cycle T [min] yield
TON
1
2
3
4
5
45
60
60
90
90
99
99
99
99
97
99
6
180
180
240
300
360
99
98
99
99
97
592
690
789
198
297
396
493
7
8
9
1089
1189
10
a
Reactions were performed under air in a CEM Discover S-Class
microwave synthesizer at 160 °C through moderation of the initial
power (300 W). A 1 mmol amount of the corresponding alkynol was
used (1 mL of water). [Substrate]/[Ag] ratio = 100:1. Determined by
b
c
GC. Cumulative TON values (turnover number = (mol of product/
mol of Ag)).
F
dx.doi.org/10.1021/ic400511d | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3
13C{1H} NMR ((CD3)2CO): δ 15.63 (d, JCP = 9.7 Hz,
CONCLUSION
■
1
3
OCH2CH3), 53.49 (dd, JCP = 50.6 Hz, JCP = 2.8 Hz, PCH2N),
64.60 (d, 2JCP = 7.4 Hz, OCH2CH3), 71.98 (d, 3JCP = 9.9 Hz, NCH2N)
ppm. 5b: Yield 79% (0.603 g). Anal. Calcd for
AgC18H22F6N4O2P2SbS: C, 28.30; H, 2.90; N, 7.33. Found: C,
28.22; H, 2.96; N 7.40. Conductivity (acetone, 20 °C): 110
Ω−1·cm2·mol−1. IR (KBr, cm−1): ν 584 (w), 605 (s), 639 (s), 714
(m), 760 (m), 797 (m), 827 (m), 903 (m), 939 (m), 991 (s), 1073
(s), 1087 (w), 1127 (m), 1205 (s), 1297 (s), 1363 (m), 1412 (w),
1507 (w), 1538 (m), 1583 (w), 1669 (w), 1739 (m), 2096 (m), 2974
(m), 3041 (w). 31P{1H} NMR ((CD3)2CO): δ −28.90 (bs, Ph2P
N), 49.99 (bs, (RO)2PS) ppm. 1H NMR ((CD3)2CO): δ 4.35 (d,
6H, 2JHP = 9.7 Hz, PCH2N), 4.52 and 4.61 (AB spin system, 3H each,
JHA,HB = 13.3 Hz, NCH2N), 7.30−7.51 (m, 10H, CHarom) ppm.
13C{1H} NMR ((CD3)2CO): δ 53.58 (d, 1JCP = 51.5 Hz, PCH2N),
In summary, in the present work we described the use, for the
first time, of PTA- or DAPTA-base iminophosphorane ligands
as versatile building blocks for high-yield synthesis of a series of
new Ag(I) coordination polymers [Ag{μ2-N,S-(PTA)NP(
S)(OR)2}]x[SbF6]x (R = Et (5a), Ph (5b)) and [Ag{μ2-O,S-
(DAPTA)NP(S)(OR)2}]x[SbF6]x (R = Et (6a), Ph (6b)).
To our knowledge, complexes 6a and 6b represent the first
examples in which coordination of the acetyl group of DAPTA
is achieved. In addition, we have also shown that the complex
[Ag{μ2-N,S-(PTA)NP(S)(OEt)2}]x[SbF6]x (5a), always
in neutral conditions, is a highly efficient catalyst precursor for
isomerization of both terminal and internal propargylic alcohols
into α,β-unsaturated carbonyl compounds, which can be
obtained in excellent yields in water. This catalytic system has
also proven to promote chemoselective transformations
producing enals (terminal alkynols) or enones (internal
alkynols) depending on the nature of the propargylic alcohol.
Finally, we must also note that (i) the highly effective catalyst
recycling observed using water as solvent and (ii) the total
atom economy of this process are in good agreement with the
principles of so-called “Green Chemistry”.19
3
72.59 (d, JCP = 9.5 Hz, NCH2N), 121.88−131.18 (m, CHarom),
151.74 (d, 2JCP = 8.5 Hz, Cipso of OPh) ppm. 6a: Yield 87% (0.644 g).
Anal. Calcd for AgC13H26F6N4O4P2SbS: C, 21.10; H, 3.54; N, 7.57.
Found: C, 21.17; H, 3.56; N 7.61. Conductivity (acetone, 20 °C): 110
Ω−1·cm2·mol−1. IR (KBr, cm−1): ν 483 (w), 591 (m), 623 (m), 659
(s), 702 (w), 753 (s), 781 (s), 839 (w), 894 (s), 956 (s), 989 (s), 1042
(vs), 1095 (w), 1123 (w), 1161 (m), 1223 (vs), 1261 (s), 1303 (s),
1333 (s), 1355 (m), 1428 (s), 1651 (vs), 2929 (w), 2981 (w). 31P{1H}
NMR ((CD3)2CO): δ −10.92 (d, 2JPP = 13.7 Hz, Ph2PN), 53.30
2
1
(d, JPP = 13.7 Hz, (RO)2PS) ppm. H NMR ((CD3)2CO): δ
3
1.33 (t, 6H, JHH = 6.9 Hz, OCH2CH3), 2.09 and 2.12 (s, 3H each,
EXPERIMENTAL SECTION
COCH3), 3.78 (m, 1H, NCH2N), 4.18 (m, 8H, 4H for OCH2CH3 and
4H for PCH2NCO), 4.71 and 5.10 (d, 1H each, JHH = 14.0 Hz,
■
General Comments. All reagents were obtained from commercial
suppliers and used without further purification with the exception of
compounds (PTA)NP(S)(OR)2 (R = Et (3a), Ph (3b)) and
(DAPTA)NP(S)(OR)2 (R = Et (4a), Ph (4b)), which were
prepared by the following methods reported in the literature.3
NCH2N), 4.88 (m, 1H, PCH2N), 5.66 (m, 2H, 1H for NCH2N and
3
1H for PCH2N). 13C{1H} NMR ((CD3)2CO): δ 21.27 (d, JCP
=
=
1
8.5 Hz, OCH2CH3), 26.33 and 26.74 (s, COCH3), 45.73 (dd, JCP
70.2 Hz, 3JCP = 4.0 Hz, PCH2N), 50.94 (dd, 1JCP = 69.4 Hz, 3JCP = 4.8
Hz, PCH2N), 56.05 (dd, 1JCP = 59.9 Hz, 3JCP = 2.1 Hz, PCH2N), 66.79
Propargylic alcohols 7a−h and 9a−d were obtained from commercial
suppliers or synthesized following the classical Midlands procedure.
3
2
44
and 72.02 (d, JCP = 6.9 Hz, NCH2N), 68.48 (d, JCP = 6.9 Hz,
OCH2CH3), 174.51 and 174.95 (s, COCH3) ppm. 6b: Yield 91%
(0.761 g). Anal. Calcd for AgC21H26F6N4O4P2SbS: C, 30.17; H, 3.13;
N, 6.70. Found: C, 30.10; H, 3.09; N, 6.65. Conductivity (acetone, 20
°C): 115 Ω−1·cm2·mol−1. IR (KBr, cm−1): ν 474 (w), 537 (m), 585
(m), 599 (m), 658 (m), 690 (m), 743 (s), 782 (s), 839 (m), 898 (s),
931 (s), 945 (s), 1022 (s), 1081 (m), 1170 (w), 1153 (w), 1162 (m),
1195 (w), 1212 (s), 1267 (s), 1306 (s), 1320 (s), 1359 (w), 1425 (s),
1460 (w), 1657 (vs), 1891 (w), 1965 (w), 2933 (w), 2988 (w).
́
Infrared spectra were recorded on a Perkin-Elmer 1720-XFT
spectrometer. For electrospray ionization mass spectrometry (ESI-
MS) studies, a QTOF Premier instrument with an orthogonal Z-spray-
electrospray interface (Waters, Manchester, U.K.) was used operating
in the W mode at a resolution of ca. 15 000 (fwhm). The drying and
cone gas was nitrogen set to flow rates of 300 and 30 L/h, respectively.
A capillary voltage of 3.5 kV was used in the positive scan mode, and
the cone voltage was set to Uc = 10 V. For accurate mass
measurements, a 2 mg/L standard solution of leucine enkephalin
was introduced via the lock spray needle at a cone voltage set to 45 V
and a flow rate of 30 μL/min. 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 (1H), 121.5 (31P), and 75.4
MHz (13C) using SiMe4 or 85% H3PO4 as standards. DEPT
experiments have been carried out for all compounds reported in
this paper.
2
31P{1H} NMR ((CD3)2CO): δ −14.64 (d, JPP = 21.4 Hz, Ph2P
2
N), 55.46 (d, JPP = 21.4 Hz, (RO)2PS) ppm. 1H NMR
((CD3)2CO): δ 1.99 and 2.01 (s, 3H each, COCH3), 3.50 (m,
1H, NCH2N), 4.04 (m, 4H, PCH2NCO), 4.58 and 5.51 (m, 2H each,
1H for NCH2N and 1H for PCH2N), 5.00 (d, 1H, JHH = 14.3 Hz,
NCH2N), 7.17−7.40 (m, 10H, CHarom) ppm. 13C{1H} NMR
1
((CD3)2CO): δ 21.01 and 21.40 (s, COCH3), 39.99 (dd, JCP
=
71.0 Hz, 3JCP = 4.8 Hz, PCH2N), 45.20 (dd, 1JCP = 69.4 Hz, 3JCP = 4.2
Hz, PCH2N), 50.42 (dd, 1JCP = 59.9 Hz, 3JCP = 2.7 Hz, PCH2N), 61.52
Preparations. Synthesis of Ag(I) Coordination Polymers ([Ag{μ2-
N,S-(PTA)NP(S)(OR)2}]x[SbF6]x (R = Et (5a), Ph (5b)) and [Ag{μ2-
O,S-(DAPTA)NP(S)(OR)2}]x[SbF6]x (R = Et (6a), Ph (6b)). A
solution of the corresponding iminophosphorane ligands 3a, 3b, 4a,
and 4b (1 mmol) in 30 mL of CH2Cl2 was treated with AgSbF6 (0.343
g, 1 mmol) and stirred for 1 h to yield a pale-yellow clear solution. The
solvent was then concentrated (ca. 1 mL) in vacuo, and addition of
diethyl ether (ca. 50 mL) precipitated a white solid, which was washed
with diethyl ether (3 × 10 mL) and dried in vacuo. 5a: Yield 76%
(0.508 g). Anal. Calcd for AgC10H22F6N4O2P2SbS: C, 17.98; H, 3.32;
N, 8.39. Found: C, 18.04; H, 3.29; N 8.45. Conductivity (acetone, 20
°C): 105 Ω−1·cm2·mol−1. IR (KBr, cm−1): ν 542 (w), 594 (s), 660
(vs), 744 (m), 783 (m), 818 (m), 834 (m), 907 (m), 942 (s), 972 (s),
1010 (vs), 1096 (m), 1161 (m), 1238 (s), 1299 (s), 1369 (m), 1391
(m), 1412 (m), 1447 (m), 1473 (w), 1521 (w), 1635 (w), 1700 (w),
2090 (w), 2984 (m). 31P{1H} NMR ((CD3)2CO): δ −31.94 (d, 2JPP
3
and 66.75 (d, JCP = 6.9 Hz, NCH2N), 122.05−129.73 (m, CHarom),
152.39 (d, 2JCP = 7.4 Hz, Cipso of OPh), 152.44 (d, 2JCP = 8.0 Hz, Cipso
of OPh), 169.13 (s, COCH3), 169.61 (d, 3JCP = 2.1 Hz, COCH3) ppm.
General Procedure for Catalytic Propargylic Isomerization in
Water. Under air, a pressure-resistant septum-sealed glass microwave
reactor vial was charged with the corresponding alkynol (1 mmol),
silver catalyst 5a (0.0067 g, 1 mol % of Ag), a magnetic stirring bar,
and distilled water (1 mL). The vial was then placed inside the cavity
of a CEM Discover S-Class microwave synthesizer, and power was
held at 300 W until the desired temperature (160 °C) was reached.
Microwave power was automatically regulated for the remainder of the
experiment to maintain the temperature monitored by a built-in
infrared sensor (the course of the reaction was monitored by regular
sampling and analysis by GC). The internal pressure during the
reaction ranged between 5 and 95 psi. 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 eluent. The identity of
the resulting α,β-unsaturated carbonyl compounds was assessed by
2
1
= 2.4 Hz, Ph2PN), 53.62 (d, JPP = 2.4 Hz, (RO)2PS) ppm. H
NMR ((CD3)2CO): δ 1.39 (t, 6H, 3JHH = 6.9 Hz, OCH2CH3), 4.18
2
(m, 4H, OCH2CH3), 4.47 (d, 6H, JHP = 9.4 Hz, PCH2N), 4.52 and
4.63 (AB spin system, 3H each, JHA,HB = 15.5 Hz, NCH2N) ppm.
G
dx.doi.org/10.1021/ic400511d | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
comparison of their H and 13C{1H} NMR spectroscopic data with
(l) Kirillov, A. M.; Kirillova, M. V.; Pombeiro, A. J. L. Coord. Chem.
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those reported in the literature and by their fragmentation in GC/MS.
General Procedure for Catalyst Recycling. The recyclability of the
Ag(I) complex 5a was investigated using isomerization of the
commercially available alkynol 1,1-diphenyl-2-propyn-1-ol (7a) to
3,3-diphenylpropenal (8a) as a model reaction. Under air, a pressure-
resistant septum-sealed glass microwave reactor vial was charged with
the alkynol 7a (0.208 g, mmol), silver catalyst 5a (0.0067 g, 1 mol % of
Ag), a magnetic stirring bar, and distilled water (1 mL). The vial was
then placed inside the cavity of a CEM Discover S-Class microwave
synthesizer, and power was held at 300 W until the desired
temperature (160 °C) was reached. Microwave power was automati-
cally regulated for the remainder of the experiment to maintain the
temperature monitored by a built-in infrared sensor (the course of the
reaction was monitored by regular sampling and analysis by GC). The
internal pressure during the reaction ranged between 5 and 95 psi.
Complete consumption of 7a was observed after 45 min. Aqueous
phase was extracted with diethyl ether (3 × 5 mL). To the aqueous
layer, 0.208 g (1 mmol) of alkynol 7a was again added, and the
mixture was stirred again under the same conditions for the required
time. This procedure was repeated up to 10 consecutive times.
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F. C.; Pombeiro, A. J. L. Organometallics 2009, 28, 1683. (e) Jaremko,
Ł.; Kirillov, A. M.; Smolenski, P.; Pombeiro, A. J. L. Cryst. Growth Des.
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dez-Barbero, A. Angew. Chem., Int. Ed. 2008, 47, 8665.
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(j) Kirillov, A. M.; Wieczorek, S. W.; Lis, A.; Guedes da Silva, M. F. C.;
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ASSOCIATED CONTENT
* Supporting Information
Crystallographic data for 5b and 6a, ESI-MS spectrum of an
aqueous solution of complex 5a, and micrographs of the silver
nanoparticles (TEM and SEM images). This material is
available free of charge via the Internet at http://pubs.acs.org.
■
C. Eur. J. Inorg. Chem. 2012, 5854.
S
(4) See, for example: (a) Trost, B. M. Science 1991, 254, 1471.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: garciajoaquin@uniovi.es.
Notes
■
The authors declare no competing financial interest.
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
2004. (h) Escher, I.; Glorius, F. In Science of Synthesis; Bruckner, R.,
̈
́
“Juan de la Cierva” and a “Ramon y Cajal” contracts. We are
Schaumann, E., Eds.; Thieme Verlag: Stuttgart, 2006; Vol. 25, pp 733−
thankful for the support of the Scientific and Technical Services
(UniOvi) X Ray Single Crystal Diffraction. The authors are also
777.
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grateful to the Serveis Centrals d’Instrumentacio Cientifica
(SCIC) of the Universitat Jaume I for providing the mass
spectrometry facilities.
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(36) It is nowadays well recognized that use of microwave (MW)
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the system takes place, thus shortening considerably the reaction times
and improving in many cases the product yields. See, for example:
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(41) Primary propargylic alcohols have proven to be very difficult
substrates for the Meyer−Schuster reaction. To our knowledge, only
one successful methodology has been described to date in the
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(42) For a recent book covering the synthesis, reactivity, and catalytic
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