Reactivity of molybdenum and rhenium hydroxo complexes toward organic electrophiles: Reactions that afford carboxylato products

Article abstract of DOI:10.1021/om051081g

The reactions of the hydroxo complexes [Mo(OH)(η³-methallyl) (CO)₂(phen)] (1) and [Re(OH)(CO)₃-(Me₂-bipy)] (2) (phen = 1,10-phenanthroline, Me₂-bipy= 4,4′-dimethyl-2, 2′-bipyridine) with maleic anhydr

Full text of DOI:10.1021/om051081g

Organometallics 2006, 25, 1717-1722
1717
Reactivity of Molybdenum and Rhenium Hydroxo Complexes
toward Organic Electrophiles: Reactions that Afford Carboxylato
Products§
Luciano Cuesta,† Eva Hevia,† Dolores Morales,† Julio Pe´rez,*,† Luc´ıa Riera,† and
Daniel Miguel‡
Departamento de Qu´ımica Orga´nica e Inorga´nica-IUQOEM, Facultad de Qu´ımica-CSIC, UniVersidad de
OViedo, OViedo 33006, Spain, and Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias,
UniVersidad de Valladolid, Valladolid 47071, Spain
ReceiVed December 20, 2005
The reactions of the hydroxo complexes [Mo(OH)(η3-methallyl)(CO)2(phen)] (1) and [Re(OH)(CO)3-
(Me2-bipy)] (2) (phen ) 1,10-phenanthroline, Me2-bipy) 4,4′-dimethyl-2,2′-bipyridine) with maleic
anhydride, phenyl(ethyl)ketene, diphenylketene, and rac-lactide afford new carboxylato complexes. The
molybdenum and rhenium hydroxo complexes react in the same way, and their reactions are quantitative.
The products, some of which have been characterized by X-ray diffraction, feature monodentate O-bonded
carboxylato ligands, and their treatment with triflic acid yields the triflato complexes [Mo(OTf)(η3-
methallyl)(CO)2(phen)] and [Re(OTf)(CO)3(Me2-bipy)] and the corresponding free carboxylic acid.
Scheme 1. Reaction of the Hydroxo Complexes 1 and 2
with Maleic Anhydride, and Demetalation of the Products
by Reaction with Triflic Acid
Introduction
Organometallic hydroxo complexes have attracted consider-
able interest due to their participation in industrially or biologi-
cally relevant processes, their rich coordination chemistry, and
the challenge of their synthesis.1 Hydroxo, alkoxo, or amido
groups are strongly π-donor ligands. As a result, most complexes
with these ligands are found with early transition metals and
are stabilized by the ligand-to-metal electron donation. In
contrast, late transition metal organometallic complexes with
terminal hydroxo ligands are rare, a fact initially attributed to
an inherent thermodynamic instability and that now seems rather
related to synthetic difficulties and their tendency to oligomerize.
Recently, we have found that the easily prepared and relatively
stable complexes [Mo(OH)(η3-methallyl)(CO)2(phen)] (1)2 and
[Re(OH)(CO)3(Me2-bipy)] (2)3 show a rich OH-centered reac-
tivity toward organic electrophiles, comparable to that found
for hydroxo complexes of groups 8-10.3c,4 We have previously
studied their reactivity toward carbon disulfide, esters, isocy-
anate, isothiocyanate, and dimethylacetylenedicarboxylate. Re-
activity studies of organometallic hydroxo complexes are still
very rare. Thus, as an extension of this work, here we report
the reactivity of the mentioned hydroxo complexes toward four
different carboxylic acid derivatives: a cyclic anhydride, two
ketenes, and a lactide. As it will be discussed, the hydroxo
complexes act as nucleophiles toward the organic reagents, and
the products of such reactions are monodentate carboxylato
products; therefore, this study is closely related to those
previously carried out by other groups on the reactions of carbon
dioxide with alkoxo complexes. Thus, Mandal, Ho, and Orchin
reported the reactivity of fac-[Mn(OCH3)(CO)3(dppe)],5 Da-
rensbourg and co-workers conducted a kinetic study on this
reaction,6 and Simpson and Bergman studied the reactivity of
analogous rhenium complexes.7
Results and Discussion
The molybdenum hydroxo complex 1 reacted instantaneously
with an equimolar amount of maleic anhydride in THF. The
red color of the solution faded upon reaction, and the ν(CO)
bands (1929 and 1843 cm-1 for 1) shifted to higher wavenumber
values (1957 and 1876 cm-1 for the product). The IR of the
resulting solution indicates the formation of a single molybde-
num cis-dicarbonyl compound as product. The shift to higher
ν(CO) IR bands reflects a lowering of the electron density at
the metal center, as expected for the reaction with an electro-
phile. The product [Mo(η3-methallyl){OC(O)CHdCHC(O)-
§ Dedicated to Professor Victor Riera on the occasion of his 70th birthday.
* To whom correspondence should be addressed. Fax: 34 98510 3446.
Tel: 34 98510 3465. E-mail: japm@uniovi.es.
† Universidad de Oviedo.
‡ Universidad de Valladolid.
(1) (a) Bryndza, H.; Tam, W. Chem. ReV. 1988, 88, 1163. (b) Gilje, J.
W.; Roesky, H. W. Chem. ReV. 1994, 94, 895. (c) Fulton, J. R.; Holland,
A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 35, 44.
(2) Morales, D.; Clemente, M. E. N.; Pe´rez, J.; Riera, L.; Riera, V.;
Miguel, D. Organometallics 2002, 21, 4934.
(3) (a) Gibson, D. H.; Yin, X. J. Am. Chem. Soc. 1998, 120, 11200. (b)
Gibson, D. H.; Yin, X.; Hen, H.; Mashuta, M. S. Organometallics 2003,
22, 337. (c) Cuesta, L.; Gerbino, D. C.; Hevia, E.; Morales, D.; Clemente,
M. E. N.; Pe´rez, J.; Riera, L.; Riera, V.; Miguel, D.; del R´ıo, I.; Garc´ıa-
Granda, S. Chem. Eur. J. 2004, 10, 1775.
(4) Gerbino, D. C.; Hevia, E.; Morales, D.; Clemente, M. E. N.; Pe´rez,
J.; Riera, L.; Riera, V.; Miguel, D. Chem. Commun. 2003, 328.
(5) Mandal, S. K.; Ho, D. M.; Orchin, M. Organometallics 1993, 12,
1714.
(6) Darensbourg, Lee, W.-Z.; Phelps, A. L.; Guidry, E. Organometallics
2003, 22, 5585.
(7) Simpson, R. D.; Bergman, R. G. Angew. Chem., Int. Ed. Engl. 1992,
31, 220.
10.1021/om051081g CCC: $33.50 © 2006 American Chemical Society
Publication on Web 03/01/2006

1718 Organometallics, Vol. 25, No. 7, 2006
Cuesta et al.
Scheme 2. Proposed Mechanism for the Reaction of the
Hydroxo Complexes with Maleic Anhydride
Scheme 3. Reaction of the Hydroxo Complexes with
Phenyl(ethyl)ketene and Diphenylketene, and Reaction of the
Products 5a and 6a with Triflic Acid, Affording the Triflato
Complexes and 2-Phenylbutyric Acid
strong hydrogen bond. In the 1H NMR spectrum, this hydrogen
appears as a singlet at 16.74 ppm.
The rhenium hydroxo complex 2 reacted with maleic
anhydride in CH2Cl2 in a similar way, affording the hydrogen
maleate product [Re{OC(O)CHdCHC(O)OH}(CO)2(Me2-bi-
py)] (4), which has been isolated in 86% yield and characterized
by microanalysis, spectroscopy, and X-ray diffraction (Figure
1b). The reaction was accompanied by a change in color from
orange to pale yellow and, as for the molybdenum complexes
discussed above, by a shift to higher IR ν(CO) values (1907,
1898, and 1878 cm-1 for 2, 2026, 1925, and 1903 cm-1 for 4).
1
The most informative H NMR features are the AB system
corresponding to the olefinic hydrogens (δA ) 5.88, δB ) 5.94,
J ) 12.8 Hz) and the COOH singlet at 16.43 ppm.
Figure 1. (a) Thermal ellipsoid (30%) plot of 3. (b) Thermal
ellipsoid (30%) plot of 4.
A similar reaction of a hydroxo complex with maleic
anhydride has been published by Woerpel and Bergman,10 and
reactions of maleic anhydride with metal alkoxo complexes have
OH}(CO)2(phen)] (3) could be isolated (83%) as a spectro-
scopically and analytically pure solid by in vacuo concentration
been studied by the groups of Bergman and Boncella.11
A
1
followed by precipitation with hexane. The H and 13C NMR
mechanistic proposal, in line with these precedents and with
spectra indicate that the presence of a molecular mirror plane
our recent work,3c is shown in Scheme 2.
1
is kept in the product. The H NMR spectrum features an AB
Complexes 3 and 4 do not react with the hydroxo precursors
1 and 2. The involvement of the carboxylic hydrogen in the
intramolecular hydrogen bond can be responsible for the
diminished acidity of the COOH groups of 3 and 4.
quartet (δA ) 5.34, δB ) 5.95, J ) 12.9 Hz), assigned to the
olefinic hydrogens of a ring-opened product, as depicted in
Scheme 1.
In the 13C NMR, the olefinic carbon atoms appear as low-
intensity signals at 132.9 and 130.0 ppm. The solid-state
structure of 3 was determined by X-ray diffraction on a single
crystal grown by slow diffusion of hexane into a concentrated
dichloromethane solution. The results are in agreement with the
spectroscopic data mentioned above. A thermal ellipsoid plot
is shown in Figure 1a.8
The molecule of 3 consists of a hydrogen maleate ligand
coordinated through one of the oxygens of the fully deprotonated
carboxylate group to a cis-{Mo(η3-methallyl)(CO)2(phen)}
fragment. As typically found,9 an intramolecular hydrogen bond
determines a ring-closed structure for the hydrogen maleate
ligand. The hydrogen atom involved in this hydrogen bond could
be fully refined, and the distances O‚‚‚O ) 2.459 Å and H‚‚‚O
) 1.573 Å and the O-H‚‚‚O angle ) 168.78(2)° indicate a
CDCl3 solutions of complexes 3 and 4 were allowed to react
with equimolar amounts of triflic acid in 5 mm NMR tubes.
1
The H NMR spectra showed that both reactions were instan-
taneous and quantitative, affording the triflato complexes [Mo-
(OTf)(η3-methallyl)(CO)2(phen)]12 and [Re(OTf)(CO)3(Me2-
bipy)]13 and maleic acid, identified by a singlet at 6.43 ppm
(Scheme 1).
The hydroxo complexes 1 and 2 react with phenyl(ethyl)-
ketene as shown in Scheme 3. The products are the carboxylato
(10) Woerpel, K. A.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 7888.
(11) (a) Glueck, D. S.; Winslow, L. J. N.; Bergman, R. G. Organome-
tallics 1991, 10, 1462. (b) Simpson, R. D.; Bergman, R. G. Organometallics
1992, 11, 4306. (c) Boncella, J. M.; Villanueva, L. R. J. Organomet. Chem.
1994, 465, 297.
(12) Coue, L.; Cuesta, L.; Morales, D.; Halfen, J. A.; Pe´rez, J.; Riera,
L.; Riera, V.; Miguel, D.; Connelly, N. G.; Boonyuen, S. Chem. Eur. J.
2004, 10, 1906.
(8) Full X-ray data are given in the Supporting Information as CIF.
(9) Modec, B.; Brencic, J. V. Inorg. Chem. Commun. 2004, 7, 516, and
references therein.
(13) Hevia, E.; Pe´rez, J.; Riera, L.; Riera, V.; del R´ıo, I.; Garc´ıa-Granda,
S.; Miguel, D. Chem. Eur. J. 2002, 8, 4510.

Reactions that Afford Carboxylato Products
Organometallics, Vol. 25, No. 7, 2006 1719
Scheme 4. Proposed Mechanism for the Reactions of 1 and
2 with Phenyl(ethyl)ketene and Diphenylketene
Scheme 5. Reaction of the Hydroxo Complexes 1 and 2
with Lactide, and Reactivity of the Products 7 and 8 toward
HOTf and MeOTf
spectrum of the rhenium complex 6a, the presence of the
stereogenic center gives rise to a splitting of the Me2bipy signals,
and the diasterotopic methylene hydrogens appear as two
multiplets at 1.75 and 1.32 ppm. The structure of 6a was
determined by X-ray diffraction, and a thermal ellipsoid plot is
shown in Figure 2a.8
Analogous reactions took place with diphenylketene (see
Scheme 3). The products [Mo(η3-C3H4-Me-2){OC(O)CH(Ph)2}-
(phen)(CO)2] (5b) and [Re{OC(O)CH(Ph)2}(Me2-bipy)(CO)3]
(6b) were isolated in high yield (88% and 81%, respectively)
and characterized by means of microanalysis and IR and NMR
1
spectroscopies. The H NMR spectra of 5b and 6b showed
signals for symmetric phen or Me2-bipy ligands in accordance
with the presence of a molecular mirror plane. All our attempts
to obtain single crystals of 6b suitable for X-ray diffraction were
unsuccessful. However, we found that the phen complex [Re-
{OC(O)CH(Ph)2}(phen)(CO)3] (6c), prepared in a completely
analogous manner and whose spectroscopic data support a
structure like that of 6b (see Experimental Section), afforded
X-ray quality crystals, one of which was used for the determi-
nation of the structure (see Figure 2b).
We are not aware of previously reported reactions of hydroxo
complexes with ketenes, and our recent reports of the reactivity
of ketenes with rhenium amido16 and alkylideneamido17 com-
plexes containing metal fragments similar to these included here
seem to be the more closely related examples.18 Scheme 4
displays a mechanistic rationale for the reactions, consisting of
nucleophilic attack by the undissociated hydroxo group to
generate a zwitterionic intermediate followed by a H+ migration
from the positively charged oxygen to the negatively charged
carbon.
Figure 2. (a) Thermal ellipsoid (30%) plot of 6a. (b) Thermal
ellipsoid (30%) plot of 6c.
(2-phenylbutyrato) complexes [Mo(η3-C3H4-Me-2){OC(O)CH-
(Ph)(Et)}(phen)(CO)2] (5a) and [Re{OC(O)CH(Ph)(Et)}(Me2-
bipy)(CO)3] (6a), which were isolated in yields of 85% and
74%, respectively, resulting from the formal insertion of the
ketene into the O-H bond. The addition of excess ketene does
not change the nature of the products; thus, a single insertion
is observed,14 as expected since the lone pairs on the metal-
bonded oxygen atom of 5a and 6a are stabilized by resonance
and, therefore, lack nucleophilic character.
Both compounds feature, as expected, IR ν(CO) bands higher
than those of the hydroxo precursors. In the 1H NMR in
deuterated acetonitrile, the presence of a stereogenic center in
the molybdenum complex 5a breaks the symmetry of the
methallyl and phen signals, the two diasterotopic methylene
hydrogens appear as two multiplets at 0.63 and 0.51 ppm, and
the one-hydrogen signal at 2.69 ppm, corresponding to the
hydrogen atom bonded to the stereogenic carbon, appears as a
double doublet.15 The solid-state structure of 5a was determined
by X-ray diffraction, and the results, although of poor quality,
are in accord with the solution data and confirm the conectivity
Complexes 5a and 6a were treated with equimolar amounts
1
of HOTf in CDCl3, and H NMR monitoring of the reactions
indicated the instantaneous and quantitative formation of the
triflato complexes [Mo(OTf)(η3-methallyl)(CO)2(phen)]12 and
[Re(OTf)(CO)3(Me2-bipy)]13 along with 2-phenylbutyric acid,
as depicted in Scheme 3.
The hydroxo complexes 1 and 2 react with rac-lactide as
indicated in Scheme 5.
(16) Hevia, E.; Pe´rez, J.; Riera, V.; Miguel, D. Organometallics 2003,
22, 257.
(17) Hevia, E.; Pe´rez, J.; Riera, V.; Miguel, D.; Campomanes, P.;
Mene´ndez, M. I.; Sordo, T. L.; Garc´ıa-Granda, S. J. Am. Chem. Soc. 2003,
125, 3706.
(18) For recent overviews of ketene chemistry, see: (a) Tidwell, T. T.
Angew. Chem., Int. Ed. 2005, 44, 5778 and 6812.
1
of the molecule as depicted in Scheme 3. In the H NMR
(14) Zhang, C.; Liu, R.; Zhou, X.; Chen, Z.; Weng, L.; Lin, Y.
Organometallics 2004, 23, 3246.
(15) In CD2Cl2 some signals appear overlapped.

1720 Organometallics, Vol. 25, No. 7, 2006
Cuesta et al.
(OTf)(CO)3(Me2-bipy)]13 along with an equivalent of lactyl-
lactic acid, while employment of MeOTf instead afforded methyl
lactyl-lactate, as shown in Scheme 5.
In summary, the hydroxo complexes [Mo(OH)(η3-methallyl)-
(CO)2(phen)] (1) and [Re(OH)(CO)3(Me2-bipy)] (2) react with
maleic anhydride, phenyl(ethyl)ketene, diphenylketene, and rac-
lactide. The reactions are quantitative, affording metal-carboxy-
late products consistent with initial nucleophilic attack by the
OH ligand. The products were characterized by spectroscopy,
X-ray diffraction, and demetalation of the corresponding car-
boxylic acids upon reaction with HOTf. From the synthetic point
of view, the chemistry reported here offers a new method to
access monodentate carboxylato complexes using reagents
soluble in organic solvents, reactions that proceed under mild
conditions, and clean processes without side-products.
Experimental Section
General conditions were given elsewhere.3c The hydroxo com-
plexes 12 and 2,3 phenyl(ethyl)ketene,20 and diphenylketene21 were
prepared according to literature procedures. Other reagents were
Figure 3. Thermal ellipsoid (30%) plot of [Re{OC(O)C(Me)OC-
(O)C(Me)OH}(Me2-bipy)(CO)3] (8).
Scheme 6. Proposed Mechanisms for the Reaction of the
Hydroxo Complexes with Lactide
1
purchased and used as received. H NMR (300 or 400 MHz) and
13C NMR spectra were recorded on a Bruker Advance 300, DPX-
300, or Advance 400 spectrometer. Elemental analyses were carried
out on a Fisons EA-1108 analyzer (C, H, and N) at the analytical
services of the Universidad de Vigo (Vigo, Spain).
Crystal Structure Determination. General Description. Com-
pounds 3 and 8: A crystal was attached to a glass fiber and
transferred to a Bruker AXS SMART 1000 diffractometer with
graphite-monochromatized Mo KR X-radiation and a CCD area
detector. A hemisphere of the reciprocal space was collected up to
2θ ) 48.6°. Raw frame data were integrated with the SAINT22
program. An empirical absorption correction was applied with the
program SADABS.23 Compounds 4, 6a, and 6c: Data collection
was carried out on a Nonius Kappa CCD single-crystal diffracto-
meter, using Cu KR radiation. Images were collected at a 29 mm
fixed crystal-detector distance, using the oscillation method, with
2° oscillation and 60 s exposure time per image. Data collection
strategy was calculated with the program Collect.24 Data reduction
and cell refinement were performed with the programs HKL Denzo
and Scalepack.25 Unit cell dimensions were determined from
reflections between θ ) 2° and 70°. A semiempirical absorption
correction was applied using the program SORTAV.26 Structure
solution and refinement (all): The structures were solved by direct
methods with SHELXTL.27 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were set in calculated positions
and refined as riding atoms with a common thermal parameter.
Calculations were made with SHELXTL and PARST.28
The IR spectra of the products, [Mo(η3-C3H4-Me-2){OC(O)C-
(Me)OC(O)C(Me)OH}(phen)(CO)2] (7) and [Re{OC(O)C(Me)-
OC(O)C(Me)OH}(Me2-bipy)(CO)3] (8), showed the expected
increase in the wavenumber values of the carbonyl stretching
bands. The 1H NMR spectra featured, in addition to the signals
of the chelate ligand, the expected two CH quartets and two
CH3 doublets for the resulting carboxylato (lactyl-lactato) ligand.
The 13C NMR spectrum could be acquired for the more soluble
product 8 and was consistent with the formulation given in
Scheme 5. The structure of 8 was confirmed by X-ray
diffraction, and the thermal ellipsoid plot is shown in Figure
3.8
We are not aware of previous reports of stoichiometric
reactions between lactides and transition metal hydroxo com-
plexes, in contrast with the extensive studies conducted on the
polymerization of lactides initiated by main group complexes.19
Complexes 7 and 8 do not react with excess lactide.
Scheme 6 shows the two possible mechanisms that can be
considered for the reaction, by analogy with proposals made in
the context of the mentioned studies of the main group
compounds.
Compounds 3 and 6a crystallize in non-centrosymmetric space
groups. Statistics on normalized factors calculated during the data
reduction process suggested an acentric distribution of intensities,
which was confirmed in the refinement stage. The Flack parameter29
(20) Baigrie, L. M.; Seiklay, H. R.; Tidwell, T. T. J. Am. Chem. Soc.
1985, 107, 5391.
(21) Taylor, E. C.; McKillop, A.; Hawks, G. H. Org. Synth. 1980, 6,
549.
(22) SAINT+, SAX area detector integration program, Version 6.02;
Bruker AXS, Inc.: Madison, WI, 1999.
(23) Sheldrick, G. M. SADABS, Empirical Absorption Correction Pro-
gram; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(24) Collect; Nonius BV: Amsterdam, 1997-2004.
(25) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(26) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(27) Sheldrick, G. M. SHELXTL, An integrated system for solving,
refining, and displaying crystal structures from diffraction data, Version
5.1; Bruker AXS, Inc.: Madison, WI, 1998.
Complexes 7 and 8 react with HOTf, affording the triflato
complexes [Mo(OTf)(η3-methallyl)(CO)2(phen)]12 and [Re-
(19) (a) Aida, T.; Inoue, S. Acc. Chem. Res. 1996, 29, 39. (b) O’Keefe,
B. J.; Hillmyer, M. A.; Tolman, W. B. Dalton Trans. 2001, 2215. (c) Coates,
G. W. Dalton Trans. 2002, 467. (d) Bourissou, D.; Martin-Vaca, B.;
Dumitrescu, A.; Graullier, M.; Lacombe, F. Macromolecules 2005, 38, 9993.
(e) Bonnet, F.; Cowley, A. R.; Mountford, P. Inorg. Chem. 2005, 44, 9046.
(f) Barnea, E.; Moradove, D.; Berthet, J.-C.; Ephritikhine, M.; Eisen, M.
S. Organometallics 2006, 25, 320.
(28) (a) Nardelli, M Comput. Chem. 1983, 7, 95. (b) Nardelli, M. J. Appl.
Crystallogr. 1995, 28, 659.
(29) Flack, H. D. Acta Crystallogr. 1983, A39, 876.

Reactions that Afford Carboxylato Products
Organometallics, Vol. 25, No. 7, 2006 1721
was estimated from experimentally measured Friedel pairs and
refined to a value close to 0 for both compounds (0.00(3) from
1253 Friedel pairs for compound 3; -0.002(18) from 1884 Friedel
pairs for compound 6a).
(Ph)], 54.1 [C1 and C3 of allyl], 27.5 [CH2 of Et], 19.6 [CH3 of
allyl], 12.4 [CH3 of Et].
Synthesis of [Mo(η3-C3H4-Me-2){OC(O)CH(Ph)2}(phen)-
(CO)2] (5b). The reaction is similar to that described above for
5a, starting from Ph2CdCdO (0.035 g, 0.18 mmol) and 1 (0.070
g, 0.17 mmol). Yield: 0.090 g, 88%. Anal. Calcd for C32H26-
MoN2O4: C 64.22, H 4.38, N 4.68. Found: C 63.92, H 4.05, N,
4.84. IR (CH2Cl2): 1953vs, 1872s (νCO). 1H NMR (CDCl3): 9.12
[d (4.2 Hz), 2H, phen], 8.35 [dd (8.1, 1.1 Hz), 2H, phen], 7.83 [s,
2H, phen], 7.67 [m, 2H, phen], 6.68 [m, 10H, Ph], 4.51 [s, 1H,
HCPh2], 2.98 [s, 2H, Hsyn], 1.36 [s, 1H, Hanti], 0.80 [s, 3H, CH3 of
allyl].
Synthesis of [Mo(η3-C3H4-Me-2){OC(O)CHdCHC(O)OH}-
(phen)(CO)2] (3). Maleic anhydride (0.013 g, 0.13 mmol) was
added to a solution of 1 (0.050 g, 0.12 mmol) in THF (15 mL).
Immediately, the color of the solution changed from deep red to
light red. The solution was stirred for 15 min and filtered through
diatomaceous earth. In vacuo concentration and addition of hexane
(15 mL) caused the precipitation of a red microcrystalline solid,
which was washed with hexane (3 × 10 mL) and dried under
vacuum. By slow diffusion of hexane into a concentrated solution
of 3 in CH2Cl2 red needles were obtained, one of which was used
for an X-ray analysis. Yield: 0.050 g, 83%. Anal. Calcd for C22H18-
MoN2O6: C, 52.60; H, 3.61; N, 5.57. Found: C, 52.66; H, 3.82;
Synthesis of [Re{OC(O)CH(Ph)(Et)}(Me2-bipy)(CO)3] (6a).
Ph(Et)CdCdO (0.030 g, 0.20 mmol) was added to a solution of 2
(0.060 g, 0.12 mmol) in CH2Cl2 (15 mL). The color of the solution
changed from orange to yellow. The solvent was concentrated in
vacuo, and addition of hexane (20 mL) caused the precipitation of
a yellow microcrystalline solid, which was washed with diethyl
ether (2 × 10 mL) and redissolved in CH2Cl2 (10 mL). Slow
diffusion of hexane into this solution at -20 °C afforded yellow
crystals, one of which was employed for an X-ray structure
determination. Yield: 0.057 g, 74%. Anal. Calcd for C25H23N2O5-
Re: C 48.61, H 3.75, N 4.53. Found: C 48.69, H 3.61, N 4.49. IR
1
N, 5.30. IR (THF): 1957vs, 1876vs (νCO). H NMR (CD2Cl2):
16.74 [s, 1H, C(O)OH], 9.36 [m, 2H, phen], 8.57 [d (7.9 Hz), 2H,
phen], 8.00 [s, 2H, phen], 7.91 [m, 2H, phen], 5.34, 5.95 [AB (12.9
Hz), 2H, HCdCH], 3.17 [s, 2H, Hsyn], 1.44 [s, 2H, Hanti], 0.82 [s,
3H, η3-C3H4(CH3)-2]. 13C NMR (CD2Cl2): 223.1 [2×CO], 172.1,
165.8 [2×C(O)O], 152.5, 149.9, 138.4,135.6 [phen], 132.9, 130.0
[HCdCH], 127.4, 124.8 [phen], 81.1 [C2 of allyl], 54.3 [C1 and C3
of allyl], 18.9 [CH3 of allyl].
1
(CH2Cl2): 2017vs, 1912s, 1888s (νCO). H NMR (CD2Cl2): 8.83
[m, 2H, Me2-bipy], 7.67 [s, 1H, Me2-bipy], 7.60 [s, 1H, Me2-bipy],
7.29-7.20 [m, 2H, Me2-bipy], 7.09-6.90 [m, 3H, Ph], 6.63-6.61
[m, 2H, Ph], 2.87 [t (7.6 Hz), 1H, CH(Et)(Ph)], 2.51 [s, 3H, Me2-
bipy ], 1.75 [m, 1H, CH2 of Et], 1.32 [m, 1H, CH2 of Et], 0.57 [t
(7.2 Hz), 3H, CH3 of Et]. 13C NMR (CD2Cl2): 201.1, 196.9, 190.8
[1 CO each], 179.7 [C(O)O], 157.6, 157.3, 155.3, 155.0, 153.7,
153.5 [Me2-bipy], 145.3, 130.7, 129.9, 129.7 [Ph], 128.3, 127.5
[Ph], 125.7, 125.6 [Me2-bipy], 58.1 [C(H)(Et)(Ph)], 29.1 [CH2 of
Et], 23.8, 23.7 [Me2-bipy], 14.5 [CH3 of Et].
Synthesis of [Re{OC(O)CH(Ph)2}(Me2-bipy)(CO)3] (6b). The
procedure was as described for 6a, using Ph2CdCdO (0.025 g,
0.13 mmol) and 2 (0.060 g, 0.12 mmol). The color of the solution
changed instantaneously from orange to yellow. Yield: 0.054 g,
81%. Anal. Calcd for C29H23N2O5Re: C 52.32, H 3.48, N 4.21.
Found: C 51.99, H 3.33, N 4.17. IR (CH2Cl2): 2020vs, 1911s,
1897s (νCO). 1H NMR (CD2Cl2): 8.87 [d (5.6 Hz), 2H, Me2-bipy],
7.72 [s, 2H, Me2-bipy], 7.72 [d (5.6 Hz), 2H, Me2-bipy], 7.10 [m,
2H, Ph], 7.04 [m, 4H, Ph], 6.87 [m, 4H, Ph], 4.52 [s, 1H, HCPh2],
2.51 [s, 3H, Me2-bipy ].
Synthesis of [Re{OC(O)CH(Ph)2}(phen)(CO)3] (6c). The
procedure was as described for 6a and 6b, using [Re(OH)(CO)3-
(phen)] (0.060 g, 0.12 mmol) and Ph(Et)CdCdO (0.025 g, 0.13
mmol). The color of the solution changed immediately from orange
to yellow. Slow diffusion of hexane into a solution of 6c in CH2-
Cl2 at room temperature afforded yellow crystals, one of which
was suitable for an X-ray analysis. Yield: 0.052 g, 78%. Anal.
Calcd for C29H19N2O5Re: C 52.65, H 2.89, N 4.23. Found: C
52.70, H 3.02, N 4.11. IR (CH2Cl2): 2021vs, 1914s, 1904s (νCO).
1H NMR (CD2Cl2): 9.35 [m, 2H, phen], 8.47 [m, 2H, phen], 7.99
[s, 2H, phen], 7.78 [m, 2H, phen], 6.81 [m, 2H, Ph], 6.77 [m, 4H,
Ph], 6.31 [m, 4H, Ph], 4.49 [s, 1H, HCPh2].
Synthesis of [Re{OC(O)CHdCHC(O)OH}(Me2-bipy)(CO)3]
(4). Maleic anhydride (0.010 g, 0.10 mmol) was added to a solution
of 2 (0.050 g, 0.10 mmol) in CH2Cl2 (15 mL). The color of the
solution changed instanteously from orange to light yellow. The
solvent was removed in vacuo to a volume of 5 mL, and addition
of hexane (20 mL) caused the precipitation of a yellow micro-
crystalline solid, which was washed with hexane (10 mL) and
redissolved in CH2Cl2 (5 mL). Slow diffusion of diethyl ether into
this solution at room temperature afforded yellow crystals of 4,
one of which was employed for an X-ray structure determination.
Yield: 0.051 g, 86%. Anal. Calcd for C19H15ReN2O7: C, 40.07;
H, 2.65; N, 4.91. Found: C, 40.36; H, 2.82; N, 5.20. IR (CH2Cl2):
1
2026vs, 1925s, 1903s (νCO). H NMR (CD2Cl2): 16.40 [s, C(O)-
OH], 8.89 [d(5.5 Hz), 2H, Me2-bipy], 8.00 [d(5.5 Hz), 2H, Me2-
bipy], 5.88, 5.94 [AB (12.8 Hz), 2H, HCdCH], 2.56 [s, 6H, Me2-
bipy].13C NMR (CD2Cl2): 197.8. [2×CO], 194.0 [CO], 172.5, 166.0
[2×C(O)O], 155.9, 153.6, 152.9 [Me2-bipy], 135.2, 133.9 [HCd
CH], 128.4, 124.2 [Me2-bipy], 21.9 [Me2-bipy].
Reactions of 3 and 4 with HOTf. NMR tubes of 5 mm were
charged with solutions of 3 (0.024 g, 0.045 mmol) and 4 (0.027 g,
0.045 mmol), respectively, in 0.6 mL of CDCl3 and capped with
rubber septa. HOTf (4 µL, 0.045 mmol) was injected in each tube,
1
1
and the reaction was monitored by H NMR. After 5 min the H
NMR spectra showed the 6.43 singlet of maleic acid and the signals
of the corresponding triflato complexes [Mo(η3-C3H4-Me-2)(OTf)-
(phen)(CO)2]12 and [Re(OTf)(Me2-bipy)(CO)3].13
Synthesis of [Mo(η3-C3H4-Me-2){OC(O)CH(Ph)(Et)}(phen)-
(CO)2] (5a). Ph(Et)CdCdO (0.030 g, 0.20 mmol) was added to a
solution of 1 (0.054 g, 0.13 mmol) in THF (15 mL), and the red
mixture was stirred for 15 min. The solvent was removed in vacuo,
and the residue was washed with diethyl ether (2 × 15 mL). Slow
diffusion of hexane into a CH2Cl2 solution of 5 at -20 °C afforded
red crystals, one of which was used for X-ray analysis. Yield: 0.060
g, 85%. Anal. Calcd for C28H26MoN2O4‚CH2Cl2: C 54.82, H 4.44,
N 4.41. Found: C 54.54, H 4.65, N 4.25. IR (CH2Cl2): 1948vs,
[Re(OH)(CO)3(phen)] was prepared following the procedure
described for [Re(OH)(CO)3(Me2-bipy)],3 using [Re(OTf)(CO)3-
(phen)] (0.200 g, 0.33 mmol) and KOH (0.085 mL of a solution 4
M in H2O). Yield: 0.132 g, 84%. Anal. Calcd for C15H9N2O4Re:
C 38.46, H 1.94, N 5.98. Found: C 38.27, H 2.81, N 5.81. IR
1
1861s (νCO). H NMR (CD3CN): 9.13 [m, 2H, phen], 8.62 [m,
1
(CH2Cl2): 2009vs, 1899s, 1890s (νCO). H NMR (CD2Cl2): 9.41
2H, phen], 8.04 [s, 2H, phen], 7.84 [m, 2H, phen], 6.45 [m, 5H,
Ph], 3.12 [s, 2H, Hsyn], 2.69 [dd (9.4, 9.1 Hz), 1H, CH(Et)], 1.26
[s, 1H, Hanti], 1.24 [s, 1H, Hanti], 0.87 [s, 3H, CH3 of allyl], 0.63
[m, 1H, CH2 of Et], 0.51 [m, 1H, CH2 of Et], 0.20 [t (7.24 Hz),
3H, CH3 of Et]. 13C NMR (CD2Cl2): 227.9 [2×CO], 177.8
[C(O)O], 152.0, 145.4, 143.2, 137.9, 130.5, 127.6, 127.4, 127.2,
125.4, 124.7 [phen and Ph], 81.1 [C2 of allyl], 56.7 [C(H)(Et)-
[m, 2H, phen], 9.04 [m, 2H, phen], 8.07 [s, 2H, phen], 7.88 [m,
2H, phen], 1.16 [s, 1H, OH].
Reactions of 5a and 6a with HOTf. The reactions were
conducted as described above for the reactions of 3 and 4 with
HOTf. 2-Phenylbutyric acid was identified by comparison with a
commercial sample.

1722 Organometallics, Vol. 25, No. 7, 2006
Table 1. Crystallographic Data for 3, 4, 6a, 6c, and 8
Cuesta et al.
3
4
6a
6c
8
formula
fw
C22H18MoN2O6
502.32
C19H15N2O7Re
569.53
C25H23N2O5Re
617.65
C29H19N2O5Re
661.66
C21H21N2O8Re
615.60
cryst syst
space group
a, Å
b, Å
c, Å
orthorombic
P2(1)2(1)2(1)
10.027(2)
10.868(2)
19.014(4)
90
90
90
2072.1(8)
4
triclinic
P1h
orthorombic
P2(1)2(1)2
14.416(3)
17.067(3)
9.793(2)
90
90
90
2409.4(8)
4
triclinico
P1h
monoclinic
C2/c
12.6148(15)
10.8812(13)
32.845(4)
90
96.889(2)
90
4475.9(9)
8
6.2719(13)
9.939(2)
16.062(3)
98.90(3)
96.82(3)
99.61(3)
964.4(3)
2
10.380(2)
10.971(2)
11.236(2)
93.73(3)
95.36(3)
105.83(3)
1220.2(4)
2
R, deg
â, deg
γ, deg
V, Å3
Z
T, K
293(2)
1.610
1016
293(2)
1.961
548
293(2)
1.703
1208
293(2)
1.801
644
299(2)
1.827
2400
Dc, g cm-3
F(000)
λ(Mo KR), Å
cryst size, mm
µ, mm-1
scan range, deg
no. of reflns measd
no. of indep reflns
no. of data/restraints/params
goodness-of-fit on F2
R1/Rw2 [I>2σ(I)]
R1/Rw2 (all data)
0.71073
0.13 × 0.16 × 0.28
0.675
2.14 e θ e 23.28
9153
2976
2976/0/286
1.054
0.0189/0.0478
0.0201/0.0485
1.54184
0.30 × 0.10 × 0.05
12.731
2.82 e θ e 68.58
5014
3502
3502/0/269
1.078
0.0379/0.1004
0.0388/ 0.1015
1.54184
0.10 × 0.07 × 0.05
10.181
4.01 e θ e 68.25
4399
2461
4399/0/302
1.030
0.0517/0.1302
0.0556/0.1364
1.54184
071073
0.10 × 0.07 × 0.07
0.14 × 0.37 × 0.41
10.110
5.479
3.97 e θ e 68.23
17 155
4361
4064/0/335
1.355
0.0338/0.0849
0.0369/0.0873
1.25 e θ e 23.27
9745
3224
3224/0/295
1.418
0.0694/ 0.1664
0.0730/ 0.1760
Synthesis of [Mo(η3-C3H4-Me-2){OC(O)C(Me)OC(O)C(Me)-
OH}(phen)(CO)2] (7). rac-3,6-Dimethyl-1,4-dioxan-2,5-dione (0.022
g, 0.15 mmol) was added to a solution of 1 (0.060 g, 0.15 mmol)
in THF (15 mL) and stirred for 12 h. The red solution was filtered
through diatomaceous earth, concentrated in vacuo to a volume of
5 mL, and layered with hexane, affording after slow diffusion at
room temperature red needles of 7. Yield: 0.060 g, 80%. Anal.
Calcd for C24H24MoN2O7: C, 52.56; H, 4.41; N, 5.11. Found: C,
52.32; H, 4.60; N, 5.01. IR (THF): 1954vs, 1870vs (νCO). 1H NMR
(CD2Cl2): 9.26 [dd (3.5, 1.6 Hz), 2H, phen], 8.54 [dd (6.7, 1.3
Hz), 2H, phen], 7.99 [s, 2H, phen], 7.88 [m, 2H, phen], 4.31 [q
(7.1 Hz), 1H, CH(CH3)], 3.84 [q (7.1 Hz), 1H, CH(CH3)], 3.10 [s,
2H, Hsyn], 2.46 [s br, 1H, OH], 1.83 [s, 2H, Hanti], 1.59 [s, 3H, CH3
of allyl], 1.08 [d (7.1 Hz), 3H, CH(CH3)], 0.57 [d (7.1 Hz), 3H,
CH(CH3)].
described above, using 7 (0.022 g 0.038 mmol), 8 (0.024 g, 0.038
mmol), and HOTf (3 µL, 0.034 mmol). After 5 min, the 1H NMR
spectra showed signals for lactyl-lactic acid,30 the corresponding
triflato complexes, and small amounts of unreacted 7 or 8. Less
than the stoichiometric amounts of triflic acid had to be used;
otherwise, acid-catalyzed cyclization of lactyl-lactic acid to the
starting lactide was observed.
Reactions of 7 and 8 with MeOTf. Two 5 mm NMR tubes
were charged with solutions of 7 (0.022 g, 0.038 mmol) and 8
(0.024 g, 0.038 mmol) in 0.6 mL of CDCl3 and capped with rubber
septa. MeOTf (4 µL, 0.039 mmol) was injected, and the reactions
were monitored by 1H NMR. After 1 h (in the case of the
molybdenum complex) and 12 h (rhenium complex), the 1H NMR
spectra showed signals for free methyl-2-(2-hydroxypropionyl)-
propionate31 and the triflato complexes.
Synthesis of [Re{OC(O)C(Me)OC(O)C(Me)OH}(Me2-bipy)-
(CO)3] (8). rac-3,6-Dimethyl-1,4-dioxan-2,5-dione (0.024 g, 0.170
mmol) was added to a solution of 2 (0.080 g, 0.169 mmol) in CH2-
Cl2 (15 mL). The mixture was stirred for 30 min, and the color of
the solution changed from orange to yellow. The solution was
concentrated under vacuum to a volume of 10 mL, layered with
hexane (20 mL), and stored at -20 °C, affording, after slow
diffusion, yellow crystals of 8, one of which was used for the
structure determination by X-ray diffraction. Yield: 0.083 g, 78%.
Anal. Calcd for C21H21N3O8Re: C, 40.97; H, 3.43; N, 4.55.
Found: C, 40.63; H, 3.11; N, 4.59. IR (CH2Cl2): 2020vs, 1915s,
1891s (νCO). 1H NMR (CD2Cl2): 8.89 [d (5.4 Hz), 2H, Me2-bipy],
7.99 [s, 2H, Me2-bipy], 7.34 [d (5.4 Hz), 2H, Me2-bipy], 4.55 [q
(7.1 Hz), 1H, CHCH3], 3.94 [q (6.9 Hz), 1H, CHCH3], 2.57 [s, 6H
Me2-bipy], 1.05 [d (7.1 Hz), 3H, CHCH3], 1.00 [d (6.9 Hz), 3H,
CHCH3]. 13C NMR (CD2Cl2): 198.9. [2×CO], 194.4 [CO], 175.0,
174.4 [2×C(O)O], 156.0, 153.6, 152.3, 128.0, 124.0 [Me2-bipy],
71.7, 66.8 [2×C(CH3)], 21.9 [Me2-bipy], 20.2, 17.6 [2×C(CH3)].
Reactions of 7 and 8 with 0.9 equiv of HOTf. These reactions
were performed in NMR tubes and 1H NMR-monitored, as
Acknowledgment. We thank Ministerio de Ciencia y
Tecnolog´ıa (grants BQU2003-08649 and BQU2002-03414) and
the European Union (European Reintegration Grant to L.R.) for
support of this work, and Ministerio de Educacio´n y Ciencia
for a FPU predoctoral fellowship (to L.C.) and for Ramo´n y
Cajal fellowships (to D.M. and L.R.). Dr. Carmen AÄ lvarez-Ru´a
is gratefully acknowleged for her generous help with X-ray
diffraction.
Supporting Information Available: X-ray crystallographic data
for compounds 3, 4, 6a, 6c, and 8 as CIF. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM051081G
(30) Espartero, J. L.; Rashkov, I.; Li, S. M.; Manolova, N.; Vert, M.
Macromolecules 1996, 29, 3535.
(31) Frimer, A. A.; Gilinsky-Sharon, P. J. Org. Chem. 1995, 60, 2796.