Reactive alkoxide complexes of groups 6 and 7 metals

Article abstract of DOI:10.1021/om010977s

Reactive alkoxide complexes of groups 6 and 7 metals were investigated. Alkoxo complexes reacted with dimethylacetylenedicarboxylate (DMAD) to afford the Z-alkenyls resulting from DMAD insertion into the M-OR bonds. Results showed that the reaction of the

Full text of DOI:10.1021/om010977s

1
750
Organometallics 2002, 21, 1750-1752
Rea ctive Alk oxid e Com p lexes of Gr ou p s 6 a n d 7 Meta ls
Eva Hevia, J ulio P e´ rez,* Luc ´ı a Riera, and V ´ı ctor Riera
Departamento de Qu ı´ mica Org a´ nica e Inorg a´ nica/ IUQOEM, Facultad de Qu ı´ mica,
Universidad de Oviedo-CSIC, 33071 Oviedo, Spain
Daniel Miguel
Departamento de Qu ı´ mica Inorg a´ nica, Facultad de Ciencias, Universidad de Valladolid,
4
7071 Valladolid, Spain
Received November 9, 2001
Summary: Easily available alkoxo complexes [M(OR)-
[M(OCH3)(CO)3(bipy)] (M ) Mn, 1; Re, 2), easily avail-
3
(
CO)3(bipy)] (M ) Mn, Re) and [Mo(OR)(η -C3H5)(CO)2-
able by reaction of sodium methoxide with [M(OTf)-
3
,4
(
phen)] react with dimethylacetylenedicarboxylate (DMAD)
(CO) (bipy)] complexes, insert smoothly dimethylacet-
3
to afford the Z-alkenyls resulting from DMAD insertion
into the M-OR bonds. Evidence suggesting a nondisso-
ciative mechanism is presented.
ylenedicarboxylate (DMAD), a reaction so far exclusive
of the isoelectronic highly reactive compound [Ir(C5Me5)-
5,6
(OH)(Ph)(PMe3)].
The reactions afforded as single products the Z-
In contrast with the wealth of information available
alkenyls 5 and 6 (see Scheme 1), which were character-
ized spectroscopically and, in the case of 6, by X-ray
on the insertion of acetylenes into M-H and M-C
bonds, few examples of insertion of acetylenes into
7
1
metal-heteroatom bonds are known.1
diffraction (Figure 1). H NMR monitoring of the
insertion reaction in CD2Cl2 showed 5 and 6 to be the
only products.
Low-valent transition metal alkoxo complexes are still
rare, and the mismatch between the electron-rich metal
center and the π-donor alkoxide holds potential as a
source of reactivity. In the vast field of carbonyl-
stabilized, electron-precise middle transition metal com-
pounds, alkoxides are particularly scant. A notable
exception is Bergman’s work on [Re(OR)(CO)3L2] (L2 )
two phosphines or a bidentate phosphine or arsine)
complexes, which have been shown to insert CO2 and
We wished to extend the combination of ease of
preparation and relative stability with a high reactivity
displayed by 1 and 2 to other metal-ligand sets. We
recently found that carbanionic nucleophiles react with
3
[
MoCl(η -C3H5)(CO)2(N-N)] (N-N ) bipy, phen) com-
8
plexes to yield stable alkyls. Similarly, the reaction of
3
[
MCl(η -C3H5)(CO)2(phen)] (M ) Mo, W) with sodium
3
2
methoxide afforded the new complexes [M(OCH3)(η -
C3H5)(CO)2(phen)] (M ) Mo, 3; W, 4) which have been
CS2.
Chelating diimines such as 2,2′-bipyridine (bipy) and
,10-phenanthroline (phen) ligands are stronger electron
4
characterized spectroscopically. Alkoxide attack to the
1
allyl ligand was not observed, and complexes 3 and 4
donors than diphosphines or diarsines, as reflected in
the lower νCO values of their similar complexes (see
below). Since a more electron-rich metal center en-
hances the reactivity of alkoxide complexes toward
1
(
3) The νCO bands of 2 occur at 1999, 1882, and 1861 cm- in KBr,
3 3 3 2
in which medium the complex [Re(OCH )(CO) (PMe ) ] absorbs at 2012
and 1921 cm- (see ref 2b). This indicates the more electron-rich nature
1
2
b
of the diimine complex.
electrophiles, diimine complexes of the type [M(OR)-
CO)3(N-N)] are expected to be more reactive than their
(
4) The methoxo complexes 1-4 were prepared by reaction of
(
complexes ([M(OTf)(CO) (bipy)], M ) Mn, Re (in turn prepared by
3
3
phosphine or arsine counterparts. The planarity and
lack of bulky substituents on the diimine rings should
contribute to a higher reactivity by facilitating the
approach of the incoming electrophile to the alkoxide
group. We therefore reasoned that alkoxo complexes
with the diimine ligands could insert a broader range
of substrates. Thus, we were pleased to find that
reaction of the bromides with silver triflate); [MCl(η -C
phen)], M ) Mo, W) with sodium methoxide in dicloromethane. Full
experimental details are given as Supporting Information.
3 5 2
H )(CO) -
(
(5) Woerpel, K. A.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115,
888-7889. For insertion of acetylenes into Rh-O bonds of a bidentate
7
phosphine-alkoxide ligand see: Yamamoto, Y.; Hang, X. H.; Ma, J . F.
Angew. Chem., Int. Ed. 2000, 39, 1965-1968.
(6) To a solution of 1 (0.050 g, 0.153 mmol) in THF (20 mL) was
added DMAD (19 µL, 0.153 mmol). After stirring for 10 min the
volatiles were removed in vacuo and the residue was washed with
hexane (2 × 10 mL) to afford the complex 5. Yield: 0.057 g, 80%. IR
1
*
(
Correspondence author: (E-mail) japm@sauron.quimica.uniovi.es.
1) (a) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163-1188.
b) Villanueva, L. A.; Abboud, K. A.; Boncella, J . M. Organometallics
992, 11, 2963-2965. (c) Vanderlende, D. D.; Abboud, K. A.; Boncella,
(THF): 2009, 1915 (νCO), 1731, 1713. H NMR (CD
2
Cl
2
): 9.03, 8.05,
7.95, 7.43 [m, 2H each, bipy], 3.59 [s, 3H, CO
2
Me], 3.53 [s, 3H, CO
): 223.79 [2CO], 215.57
], 162.14 [CdC], 155.30, 154.34
[bipy], 147.72 [CdC] 137.62, 125.54, 121.79 [bipy], 59.96 [OCH ], 51.58
and 50.13 [COOCH ].
(7) X-ray data for 6: crystal dimensions 0.25 × 0.22 × 0.20 mm,
monoclinic, P2 /c, a ) 9.224(1) Å, b ) 16.112(2) Å, c ) 14.820(2) Å, â
) 97.487(3)°, V ) 2183.6(6) Å , Z ) 4, T ) 295 K, Fcalcd ) 1.824 g cm
2
-
1
3
1
(
1
Me], 2.85 [s, 3H, OMe]. C{ H} NMR (CD
[CO], 175.01 and 167.04 [OdC-OCH
2 2
Cl
3
J . M. Inorg. Chem. 1995, 34, 5319-5326. (d) Simpson, R. D.; Bergman,
R. G. Angew. Chem., Int. Ed. Engl. 1992, 31, 220-223. Examples of
alkoxocomplexes of groups 6 and 7 in low oxidation states are
referenced in this paper. (e) Boncella, J . M.; Eve, T. M.; Rickman, B.;
Abboud, K. A. Polyhedron 1998, 17, 725-736.
3
3
1
3
-3
,
-1
(2) (a) Simpson, R. D.; Bergman, R. G. Organometallics 1993, 12,
µ ) 5.613 mm , F(000) ) 1160, θmax ) 23.28°, hkl ranges -10 to 10,
7
1
1
81-796. (b) Simpson, R. D.; Bergman, R. G. Organometallics 1992,
1, 4306-4315. (c) Simpson, R. D.; Bergman, R. G. Organometallics
992, 11, 3980-3993. In a previous work, Orchin studied the CO
-17 to 17, -10 to 16; 9623 data collected, 3137 unique data (Rint )
2
0.0214), 2807 data with I > 2σ(I), 283 parameters refined, GOF(F ) )
1.108, final R indices R1 ) 0.0372, wR2 ) 0.0898; max./min. residual
3
insertion in the Mn-OMe and Re-OMe bonds of related compounds:
electron density 1.328 (0.100)/-0.968 (0.100) e Å .
Mandal, S. K.; Ho, D. M.; Orchin, M. Inorg. Chem. 1991, 30, 2244-
(8) P e´ rez, J .; Riera, L.; Riera, V.; Garc ´ı a-Granda, S.; Garc ´ı a-
2
248.
Rodriguez, E. J . Am. Chem. Soc. 2001, 123, 7469-7470.
1
0.1021/om010977s CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/26/2002

Communications
Organometallics, Vol. 21, No. 9, 2002 1751
F igu r e 2. Molecular structure of 7 with hydrogen atoms
omitted for clarity. Thermal ellipsoids are drawn at the
F igu r e 1. Molecular structure of 6 with hydrogen atoms
omitted for clarity. Thermal ellipsoids are drawn at the
3
0% probability level. Selected bond lengths (Å) and angles
(deg): Mo(1)-C(6) 2.272(5), C(6)-C(7) 1.327(7), C(7)-O(7)
3
0% probability level. Selected bond lengths (Å) and angles
1
1
1
1
.405(6); C(7)-C(6)-C(8) 117.6(4), C(7)-C(6)-Mo(1)
27.7(4), C(8)-C(6)-Mo(1) 114.8(3), C(6)-C(7)-O(7)
20.4(5), C(6)-C(7)-C(9) 125.9(4), O(7)-C(7)-C(9)
13.0(4).
(
deg): Re(1)-C(4) 2.198(8), C(4)-C(5) 1.333(12), C(5)-
O(10) 1.297(12); C(5)-C(4)-C(8) 119.4(8), C(5)-C(4)-
Re(1) 123.5(6), C(8)-C(4)-Re(1) 117.0(6), O(10)-C(5)-C(4)
1
1
24.6(9), O(10)-C(5)-C(6) 114.4(9), C(4)-C(5)-C(6)
20.5(9).
Bergman found that nucleophilic attack by the un-
Sch em e 1
dissociated alkoxide is the most plausible mechanism
for the insertion of electrophiles into Re-O bonds of the
aforementioned phosphine or arsine complexes.2 This
seems to be also the case for the reaction of DMAD with
,12
1
-3. Thus, we prepared the complex [Re(OEt)(CO)3-
(
bipy′)] (bipy′ ) 4,4′-dimethyl-2,2′-bipyridine) (8) and
found it to insert DMAD. A mixture of 2 and 8 was
dissolved in CD2Cl2, and NMR monitoring during a 40
min period (during which time DMAD insertion with
either complex reaches completion) showed the absence
of exchange products. The nonobserved crossover prod-
ucts have been independently synthesized (see Support-
1
have a stable geometry with mutually trans methoxide
and allyl ligands. Complex 3 reacted with DMAD in
dichloromethane at room temperature to give the inser-
ing Information), and their methoxide H NMR signals
were found to be distinguishable from those of the
observed products. Similar negative crossover experi-
ments were conducted with the molybdenum com-
9
tion product 7, characterized spectroscopically and by
X-ray diffraction (see Scheme 1 and Figure 2),10 in which
13
plexes.
a Z-alkenyl ligand like those present in 5 and 6
Although alkoxide dissociation does not seem to occur
prior to reaction with DMAD, the cost of M-OMe bond
cleavage is crucial to the reaction. Thus, although the
tungsten alkoxide 4 shows IR bands at lower wavenum-
bers than the molybdenum analogue 3, indicating more
back-bonding and therefore a more basic alkoxide,
(
obtained as the single product, as observed when the
1
11
reaction was monitored by H NMR) was found.
(
9) Following the procedure described for 5 and 6, to a solution of 3
0.050 g, 0.12 mmol) in CH Cl (20 mL) was added DMAD (20 µL, 0.16
mmol) to give in 45 min the complex 7. Yield: 0.052 g, 86%. IR (CH
(
2
2
2
-
1
Cl
H each, phen], 7.90 [s, 2H, phen], 7.77 [m, 2H, phen], 3.56 [s, 3H,
CO Me], 3.38 [s, 3H, CO Me], 3.18 [d (6.5), 2H, Hsyn], 2.89 [s, 3H, OMe],
2 2 2
): 1941, 1832 (νCO), 1703, 1689. H NMR (CD Cl ): 9.07, 8.43 [m,
2
(11) To our knowledge, the only insertion reactions of group 6
alkoxides are those reported by Darensbourg with anionic zerovalent
tungsten complexes, which insert CO : (a) Darensbourg, D. J .;
2
2
2
3
13
1
2
(
.75 [m, 1H, CH of η -C
CD Cl ): 228.88 [CO], 174.44 and 171.47 [OtC-OCH
52.22 [CdC], 153.55, 144.91, 137.20, 129.90, 127.35, and 124.37
3
H
5
], 1.61 [d (9.6), 2H, Hanti]. C{ H} NMR
2
2
3
], 162.03 and
Sanchez, K. M.; Reibenspies, J . H.; Rheingold, A. L. J . Am. Chem. Soc.
1989, 111, 7094-7103. (b) Darensbourg, D. J .; Mueller, B. L.; Reiben-
spies, J . H.; Bischoff, C. H. Inorg. Chem. 1990, 29, 1789-1791. (c)
Darensbourg, D. J .; Mueller, B. L.; Bischoff, C. J .; Chojnacki, S. S.;
Reibenspies, J . H. Inorg. Chem. 1991, 30, 2418-2424.
(12) It should be noted that the alkoxo complexes reported here do
not have sites for acetylene coordination previous to insertion, a feature
in common with the tungsten compounds of ref 11.
(13) Negative crossover experiments have been used to support a
nondissociative mechanism, see ref 2 and: Bergman, R. G. Polyhedron
1995, 14, 3227-3237. Preparation and data of the ethoxo complexes
are included in the Supporting Information.
1
2
3
1
3
[
phen], 76.20 [C of η -C
3
H
5
], 59.05 [OCH
3
], 57.89 [C and C of
3
η -C
3
H
5
], 51.31 and 50.31 [COOCH ].
3
(
10) Data for 7: crystal dimensions 0.41 × 0.32 × 0.18 mm, triclinic,
P 1h , a ) 10.198(2) Å, b ) 10.487(3) Å, c ) 13.233(3) Å, R ) 74.658(4)°,
3
â ) 73.658(4)°, γ ) 63.303(4)°, V ) 1197.4(5) Å , Z ) 2, T ) 295 K,
-3
-1
F
calcd ) 1.515 g cm , µ ) 50.594 mm , F(000) ) 556, θmax ) 23.28°,
hkl ranges -9 to 11, -11 to 10, -14 to 13; 5377 data collected, 3446
unique data (Rint ) 0.0280), 3100 data with I > 2σ(I), 310 parameters
2
refined, GOF(F ) ) 1.096, final R indices R1 ) 0.0586, wR2 ) 0.1448;
3
max./min. residual electron density 1.346 (0.120)/-1.112 (0.120) e Å .

1
752 Organometallics, Vol. 21, No. 9, 2002
Communications
Sch em e 2
Ack n ow led gm en t. We thank the Ministerio de
Ciencia y Tecnolog ´ı a and Ministerio de Educaci o´ n for
support of this work (Projects MCT-00-BQU-0220 and
PB97-0470-C02-01) and predoctoral fellowships (to E.H.
and L.R.).
Su p p or tin g In for m a tion Ava ila ble: Complete details for
the synthesis of all compounds, spectroscopic data, and X-ray
crystallographic data for 6 and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
complex 4 fails to insert DMAD, likely as a result of
the W-OR bond being stronger than Mo-OR. Insertion
of DMAD being faster with 1 than with 2 falls in the
same trend.
The reaction of the insertion products 5-7 with triflic
OM010977S
acid cleanly cleaves the metal-Calkenyl bond, thus al-
lowing demetalation of the olefin 91
4,15
and the potential
recycling of the metallic precursors (see Scheme 2).
The reactivity of compounds 1-4 with other electro-
philes is being investigated and will be reported in a
forthcoming publication.
(
15) Reaction of 5-7 with HOTf: The alkenyl (5, 6, or 7) was
dissolved in CDCl (0.5 mL) in a 5 mm NMR tube, which was then
capped with a rubber septum. The stoichiometric amount of HOTf was
injected. The H NMR spectrum of this sample showed the signals of
the triflato complexes (10, 11, and 12, respectively) as well as the
3
1
1
signals of the free olefin 9. H NMR data of 9 (CDCl
3
): 5.21 [s, 1H],
Me], 3.71 [s, 3H, CO Me].
Integration of the olefin and triflato complexes showed a 1:1 ratio.
(14) Feit, B.; Haag, B.; Kast, J .; Schmidt, R. R. J . Chem. Soc., Perkin
3.89 [s, 3H, OMe], 3.74 [s, 3H, CO
2
2
Trans. 1 1986, 2027-2036.