Tungsten-catalyzed alkyne metatheses in transition-metal coordination spheres: Versatile new syntheses of metallamacrocycles

Article abstract of DOI:10.1021/om030195u

The title reaction (10-15 mol % of (t-BuO)₃W-(≡C-t-Bu), chlorobenzene, 80°C) is applied to octahedral and square-planar 18- and 16-valence-electron rhenium, ruthenium, and platinum complexes with cis- or trans-Ph₂P(CH₂)

Full text of DOI:10.1021/om030195u

2184
Organometallics 2003, 22, 2184-2186
Tu n gsten -Ca ta lyzed Alk yn e Meta th eses in
Tr a n sition -Meta l Coor d in a tion Sp h er es: Ver sa tile New
Syn th eses of Meta lla m a cr ocycles
Eike B. Bauer,† Slawomir Szafert,‡ F. Hampel,† and J . A. Gladysz*,†
Institut fu¨r Organische Chemie, Friedrich-Alexander-Universita¨t Erlangen-Nu¨rnberg,
Henkestrasse 42, 91054 Erlangen, Germany, and Department of Chemistry, University of
Wroclaw, F. J oliot-Curie 14, 50-383 Wroclaw, Poland
Received March 12, 2003
Summary: The title reaction (10-15 mol % of (t-BuO)3W-
(tC-t-Bu), chlorobenzene, 80 °C) is applied to octahedral
and square-planar 18- and 16-valence-electron rhenium,
ruthenium, and platinum complexes with cis- or trans-
Ph2P(CH2)6CtCCH3 ligands. NMR analyses show ca.
90-70% educt conversions, and 17-membered diphos-
phine chelates have been isolated in 59-47% yields and
crystallographically characterized.
Here the resulting CtC linkage can be stereoselectively
reduced to either the (E)- or the (Z)-CdC isomer or
transformed to another functionality.
However, most presently available alkyne metathesis
catalysts require higher reaction temperatures, often
80-150 °C.5,6,8 Furthermore, intermediate metal alkyl-
idyne species, LnMtCR, are involved. Alkylidyne ligands
react with a broad spectrum of organic functional groups
and might be expected to be compatible with a rather
limited range of inorganic and organometallic systems
under high-temperature conditions. Indeed, the only
prior examples of alkyne metatheses in metal coordina-
tion spheres of which we are aware involve group VIII
metallocenes9sone of the most robust platforms for
organometallic chemistry. Accordingly, we selected a
standard catalyst, (t-BuO)3W(tC-t-Bu) (1),10 and set out
to investigate its reactions with alkyne-containing or-
ganometallic compounds featuring various coordination
geometries and electronic configurations.11
For initial studies, an alkyne-containing phos-
phine ligand was sought. Thus, the R,ω-dibromide
Br(CH2)6Br and NaCtCH were first reacted to give the
known terminal alkyne Br(CH2)6CtCH (2)12a in 66%
yield after workup. Terminal alkynes are normally poor
substrates for metathesis, but methylated alkynes that
can eliminate volatile 2-butyne are usually excellent
choices.5,13 Hence, 2 was treated with n-BuLi (-45 °C)
and then CH3I (0 °C) to give the known 2-alkyne
Br(CH2)6CtCCH3 (3; 71%).12b Subsequent reactions
with the diphenylphosphido nucleophiles MPPh2 (M )
Li, K) gave the target ligand Ph2P(CH2)6CtCCH3 (4)
in 81-55% yields.14
Over the past few years, alkene metathesis has been
applied with increasing frequency in inorganic and
organometallic synthesissin other words, within metal
coordination spheres.1-3 Despite the many conceivable
types of side reactions, it has proved possible to apply
Grubbs’ catalyst, Ru(dCHPh)(PCy3)2(Cl)2, to coordina-
tively unsaturated complexes, charged complexes, and
species containing CtC linkages or other functionalities
known to react with alkylidene ligands. However, one
disadvantage of alkene metathesis is that mixtures of
(E)- and (Z)-CdC isomers are typically obtained.4 For
this and other reasons, increasing attention is being
focused on the sister reaction, alkyne metathesis.5-8
† Friedrich-Alexander-Universita¨t Erlangen-Nu¨rnberg.
‡ University of Wroclaw.
(1) (a) Ruwwe, J .; Mart´ın-Alvarez, J . M.; Horn, C. R.; Bauer, E. B.;
Szafert, S.; Lis, T.; Hampel, F.; Cagle, P. C.; Gladysz, J . A. Chem. Eur.
J . 2001, 7, 3931 and references therein. (b) Review: Bauer, E. B.;
Gladysz, J . A. In Handbook of Metathesis; Grubbs, R. H., Ed.; Wiley-
VCH: Weinheim, Germany, in press.
(2) Representative contributions from other groups: (a) Rapenne,
G.; Dietrich-Buchecker, C.; Sauvage, J .-P. J . Am. Chem. Soc. 1999,
121, 994. (b) Weck, M.; Mohr, B.; Sauvage, J .-P.; Grubbs, R. H. J . Org.
Chem. 1999, 64, 5463. (c) Yasuda, T.; Abe, J .; Yoshida, H.; Iyoda, T.;
Kawai, T. Adv. Synth. Catal. 2002, 344, 705. (d) Hu¨erla¨nder, D.;
Kleigrewe, N.; Kehr, G.; Erker, G.; Fro¨hlich, R. Eur. J . Inorg. Chem.
2002, 2633. (e) Ogasawara, M.; Nagano, T.; Hayashi, T. Organome-
tallics 2003, 22, 1174 and earlier studies cited therein. (f) Chu-
churyukin, A. V.; Dijkstra, H. P.; Suijkerbuijk, B. M. J . M.; Klein
Gebbink, R. J . M.; van Klink, G. P. M.; Mills, A. M.; Spek, A. L.; van
Koten, G. Angew. Chem., Int. Ed. 2003, 42, 228; Angew. Chem. 2003,
115, 238.
(3) (a) Stahl, J .; Bohling, J . C.; Bauer, E. B.; Peters, T. B.; Mohr,
W.; Mart´ın-Alvarez, J . M.; Hampel, F.; Gladysz, J . A. Angew. Chem.,
Int. Ed. 2002, 41, 1871; Angew. Chem. 2002, 114, 1951. (b) Horn, C.
R.; Mart´ın-Alvarez, J . M.; Gladysz, J . A. Organometallics 2002, 21,
5386.
(9) (a) Brizius, G.; Pschirer, N. G.; Steffen, W.; Stitzer, K.; zur Loye,
H.-C.; Bunz, U. H. F. J . Am. Chem. Soc. 2000, 122, 12435 (see
compound 8e). (b) Sato, M.; Watanabe, M. Chem. Commun. 2002, 1574.
(10) Listemann, M. L.; Schrock, R. R. Organometallics 1985, 4, 74.
(11) Stoichiometric metathesis of (t-BuO)3W(tCR) species with
alkynyl and butadiynyl complexes, LnM(CtC)nR, have been reported:
(a) Latesky, S. L.; Selegue, J . P. J . Am. Chem. Soc. 1987, 109, 4731.
(b) Dembinski, R.; Szafert, S.; Haquette, P.; Lis, T.; Gladysz, J . A.
Organometallics 1999, 18, 5438.
(12) Previous data for 2 and 3: (a) Patwardhan, A. P.; Thompson,
D. H. Org. Lett. 1999, 1, 241; Langmuir 2000, 16, 10340. (b) Harms,
A. E.; Stille, J . R. Tetrahedron Lett. 1992, 33, 6565; Harms, A. E. Ph.D.
Thesis, Michigan State University, 1993.
(4) See: Lee, C. W.; Grubbs, R. H. Org. Lett. 2000, 2, 2145.
(5) Bunz, U. H. F. Acc. Chem. Res. 2001, 34, 998.
(6) (a) Fu¨rstner, A.; Guth, O.; Rumbo, A.; Seidel, G. J . Am. Chem.
Soc. 1999, 121, 11108. (b) Fu¨rstner, A.; Mathes, C.; Lehmann, C. W.
Chem. Eur. J . 2001, 7, 5299.
(7) Tsai, Y.-C.; Diaconescu, P. L.; Cummins, C. C. Organometallics
2000, 19, 5260.
(13) (a) Bray, A.; Mortreux, A.; Petit, F.; Petit, M.; Szymanska-
Buzar, T. J . Chem. Soc., Chem. Commun. 1993, 197. (b) Analogues of
5 with the terminal-alkyne-containing phosphine Ph2P(CH2)6CtCH
were prepared, but attempted metathesis did not give detectable
amounts of 8.
(8) (a) Brizius, G.; Bunz, U. H. F. Org. Lett. 2002, 4, 2829. (b) Grela,
K.; Ignatowska, J . Org. Lett. 2002, 4, 3747. (c) Miljanic´, O. S.; Vollhardt,
K. P. C.; Whitener, G. D. Synlett 2003, 29.
(14) All new compounds have been characterized by microanalysis,
NMR (1H, 13C, 31P) and IR spectroscopy, and mass spectrometry, as
described in the Supporting Information.
10.1021/om030195u CCC: $25.00 © 2003 American Chemical Society
Publication on Web 04/29/2003

Communications
Organometallics, Vol. 22, No. 11, 2003 2185
Sch em e 1. Tu n gsten -Ca ta lyzed Meta th eses of
Tr a n sition -Meta l-Con ta in in g Alk yn es
F igu r e 1. Molecular structure of 8. Key bond lengths (Å),
bond angles (deg), and torsion angles (deg): Re1-C40,
1.936(5); Re1-C20, 1.961(5); Re1-C30, 2.032(7); Re1-P2,
2.4987(10); Re1-P1, 2.5203(10); Re1-Br1, 2.6387(5); C6-
C7, 1.454(10); C7-C8, 1.171(9); C8-C9, 1.505(11); C40-
Re1-C20, 87.41(18); C40-Re1-C30, 91.97(19); C20-Re1-
C30, 90.00(19); C40-Re1-P2, 90.36(13); C20-Re1-P2,
176.85(13); C30-Re1-P2, 87.85(13); C40-Re1-P1,
171.21(12); C20-Re1-P1, 85.41(13); C30-Re1-P1,
93.09(12); P2-Re1-P1, 97.00(3); C40-Re1-Br1, 83.93(14);
C20-Re1-Br1, 90.69(14); C30-Re1-Br1, 175.80(12); P2-
Re1-Br1, 91.29(3); P1-Re1-Br1, 91.09(3); C8-C7-C6,
177.7(7); C7-C8-C9, 177.7(8); Re1-P1-C1-C2, -56.1(4);
Re1-P2-C14-C13, 65.3(4).
conditions. Workups gave the 18-valence-electron rhe-
nium and ruthenium cis-bis(phosphine) complexes 5 and
6, depicted in Scheme 1, and the square-planar 16-
valence-electron platinum trans-bis(phosphine) complex
7.14 All were obtained in analytically pure form, but no
efforts were made to optimize yields (54-30% after
chromatography). The spectroscopic properties matched
those of closely related complexes prepared earlier.1a,15,16
As shown in Scheme 1, a ca. 0.022 M chlorobenzene
solution of the rhenium complex 5 was treated with 15
mol % of 1 at 80 °C. In accord with common practice,5
nitrogen was bubbled through the solution to help
volatilize the 2-butyne. After 2 h, solvent was removed,
and a 31P NMR spectrum of the crude mixture estab-
lished a conversion of ca. 75%. Chromatography and
crystallization gave the new compound 8 in 47% yield.
The mass spectrum exhibited molecular and other ions
consistent with a macrocycle derived from intramolecu-
lar alkyne metathesis. The 1H and 13C NMR spectra
showed the absence of tCCH3 signals, and the 13C NMR
spectrum gave a single tC signal (δ 80.5, as compared
to δ 79.1 and 75.4 in 5). To unambiguously eliminate a
dimeric or oligomeric macrocycle derived from intermo-
lecular metathesis, a crystal structure was executed.
The result, shown in Figure 1, confirmed the presence
of a 17-membered macrocyclic ring.
Although many monophosphine complexes of 4
could have been prepared and evaluated in intermo-
lecular metatheses, we were attracted more by bis-
(phosphine) complexes with the potential for intramo-
lecular macrocyclizations. The rhenium, ruthenium, and
platinum species (CO)5Re(Br), (η5-C5H5)Ru(Cl)(PPh3)2,
and [Pt(µ-Cl)(C6F5)(SR2)]2 (SR2
) tetrahydrothio-
phene) are established precursors to bis(phosphine)
complexes1a,15,16 and were reacted with 4 under standard
(15) Uso´n, R.; Fornie´s, J .; Espinet, P.; Navarro, R.; Fortun˜o, C. J .
Chem. Soc., Dalton Trans. 1987, 2077.
(16) Coto, A.; Tenorio, M. J .; Puerta, M. C.; Valerga, P. Organome-
tallics 1998, 17, 4392.

2186 Organometallics, Vol. 22, No. 11, 2003
Communications
The ruthenium complex 6 was similarly treated with
10 mol % of 1. NMR analysis of the crude reaction
mixture indicated 70% conversion. Chromatography
gave the new complex 9 in 52% yield. The NMR and
mass spectral data were very similar to those of 8, and
as shown in Scheme 1, an analogous structure was
assigned. Hence, intramolecular macrocyclization ap-
pears to be general for such cis-bis(phosphine) com-
plexes, even at concentrations that are not particularly
dilute. One factor favoring intramolecular reaction may
be the PPh2 linkages. These would be expected, by
analogy to the “geminal dialkyl effect” in carbocycle
synthesis,17 to decrease the fraction of metal/Câ anti
conformers about the MPPh2-CH2Câ linkages. Cycliza-
tions of all-anti assemblies are of course impossible, and
gauche RePPh2-CH2Câ conformations are evident in
Figure 1 (torsion angles -56.1(4)/65.3(4)°).
Macrocyclizations involving antiperiplanar- or trans-
directed groups as in platinum complex 7 are intrinsi-
cally more difficult. Since the coordinative unsaturation
of 7 could have presented additional complications, we
were not optimistic of success. Nonetheless, analysis of
a reaction with 1 (15 mol %) by NMR showed 90%
conversion. Chromatography gave the new compound
10 (Scheme 1), containing an unusual trans-spanning
diphosphine chelate,18 in 59% yield. Replicate experi-
ments showed this metathesis to be more efficient than
the others above. However, no special feature that would
direct both alkynes to the same side of the platinum
square plane, thereby favoring intramolecular over
intermolecular cyclization, is obvious. The tC 13C NMR
chemical shift was in a normal region (δ 80.7), indicating
the absence of interactions with platinum.
To broaden the synthetic utility of the above reactions,
we sought to effect a CtC hydrogenation. Accordingly,
10 was treated with H2 (1 atm) in the presence of 10%
Pd/C catalyst, as shown in Scheme 1. Workup gave 11,
with a saturated carbon bridge between the phosphorus
atoms, in 87% yield. This compound was previously
prepared by an alkene metathesis/hydrogenation se-
quence and crystallographically characterized.1a Hence,
it constitutes additional evidence for the structure of
10. Macrocycles 8-11 exhibit good thermal stabilities
(e.g., chlorobenzene/80 °C; mp g162 °C) and have never
been observed to dimerize or oligomerize. When [Pt(µ-
3a
Cl)(C6F5)(SR2)]2 and the diphosphine Ph2P(CH2)14PPh2
were combined in an NMR tube in CD2Cl2 (1:1 Pt/
diphosphine ratio, ca. 0.018 M), a multitude of products
formed, as assayed by NMR and TLC. The 31P NMR
spectrum allowed an upper limit of 15% to be placed
upon the yield of 11. Thus, metathesis provides a
singularly successful route to such macrocycles.
In summary, this study has demonstrated that tung-
sten-catalyzed alkyne metathesis can be effected in a
variety of types of metal coordination spheres in much
the same manner as alkene metathesis. Macrocycles can
be readily generated, with no appreciable quantities of
byproducts in the cases examined. It can be anticipated
that these reactions can be extended to more compli-
cated and/or topologically novel systems, and additional
applications in organometallic and/or inorganic synthe-
sis will be described in future reports.
Ack n ow led gm en t. We thank the Deutsche Fors-
chungsgemeinschaft (DFG, Grant No. GL 300/1-2) and
J ohnson Matthey PMC (platinum and ruthenium loans)
for support.
Su p p or tin g In for m a tion Ava ila ble: Text and tables
giving experimental procedures and characterization data12 for
all compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
(17) (a) Sammes, P. G.; Weller, D. J . Synthesis 1995, 1205. (b)
Forbes, M. D. E.; Patton, J . T.; Myers, T. L.; Maynard, H. D.; Smith,
D. W., J r.; Schulz, G. R.; Wagener, K. B. J . Am. Chem. Soc. 1992, 114,
10978.
(18) Bessel, C. A.; Aggarwal, P.; Marschilok, A. C.; Takeuchi, K. J .
Chem. Rev. 2001, 101, 1031.
OM030195U